Plant Physiology - Assimilate Partitioning
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Questions and Answers

Which of the following is NOT a yield component in forage plants like alfalfa?

  • Weight per shoot
  • Number of plants per square meter
  • Number of shoots per plant
  • Tuber weight (correct)

    • A crop with a high harvest index indicates that a majority of the plant's energy goes towards producing economically valuable parts, such as grains or fruits.

    True (A)

    What is the formula for calculating the harvest index in rice?

    Harvest index of rice = Grain weight / Above ground biomass

    Assimilate partitioning refers to the distribution of ______ within a plant.

    <p>nutrients</p> Signup and view all the answers

    Match the following growth stages of a soybean crop with the primary locations of assimilate partitioning:

    <p>Vegetative stage = Leaf canopy Flower initiation = Stem and petiole tissues Grain filling = Pods and grains</p> Signup and view all the answers

    During the late stages of a soybean's growth, assimilates are primarily channeled to the grains while the vegetative organs experience a decline in dry matter.

    <p>True (A)</p> Signup and view all the answers

    Which of the following factors can influence a crop's yield?

    <p>All of the above (D)</p> Signup and view all the answers

    How can water deficit affect the duration of grain filling in cereal crops?

    <p>Water deficit can shorten the duration of grain filling due to premature senescence, decreasing yield.</p> Signup and view all the answers

    The rate of translocation of photosynthetic products is faster in C3 plants compared to C4 plants.

    <p>False (B)</p> Signup and view all the answers

    What is the name of the conducting tissue through which photosynthate is transported in plants?

    <p>Phloem (C)</p> Signup and view all the answers

    The efficiency of translocation in C4 plants may be related to the specialized ______ anatomy and a greater amount of phloem in their leaves.

    <p>Kranz</p> Signup and view all the answers

    What are the two main types of plant organs involved in the translocation of photosynthate? Describe their roles.

    <p>The two main types of plant organs involved in the translocation of photosynthate are sources and sinks. Source organs, such as mature leaves, produce photosynthate through photosynthesis. Sink organs, such as developing fruits, seeds, and young leaves, utilize and store photosynthate.</p> Signup and view all the answers

    If the demand for assimilates in the sinks is low, it can lead to a decrease in the rate of photosynthesis.

    <p>True (A)</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Photosynthate = Products of photosynthesis, such as sugars Translocation = Movement of photosynthate throughout the plant Source = Plant organ that produces photosynthate Sink = Plant organ that utilizes and stores photosynthate Kranz Anatomy = Specialized cell arrangement in C4 plants that enhances photosynthesis and translocation</p> Signup and view all the answers

    What is the typical unit of measurement for crop yield?

    <p>kg/ha (D)</p> Signup and view all the answers

    Which of the following factors can reduce the translocation of photosynthate in plants?

    <p>All of the above (D)</p> Signup and view all the answers

    Young leaves act as sources of photosynthate because they can fix enough carbon to support their growth.

    <p>False (B)</p> Signup and view all the answers

    What are the two main types of yield?

    <p>Biological yield and economic yield</p> Signup and view all the answers

    The economic part of the plant in cereal crops is primarily the ______.

    <p>grains</p> Signup and view all the answers

    Explain how the concentration of photosynthate in a leaf can influence the rate of photosynthesis.

    <p>The concentration of photosynthate in a leaf can influence the rate of photosynthesis through feedback mechanisms. When the concentration of photosynthate in the leaf is high, it can signal the plant to reduce photosynthesis, as there is already a surplus of carbohydrates. Conversely, when the concentration of photosynthate is low, it can signal the plant to increase photosynthesis to replenish the supply.</p> Signup and view all the answers

    Match the following crop types with their respective economic yield components:

    <p>Cereals = Grains Legumes = Pods and seeds Tuber crops = Tubers and roots Forages = Fresh or dry matter</p> Signup and view all the answers

    What is the major yield component in cereals?

    <p>weight of spikelets</p> Signup and view all the answers

    Which of the following factors influences yield in legume crops?

    <p>All of the above (D)</p> Signup and view all the answers

    What is the primary limiting factor of crop yield under optimal agronomic practices?

    <p>Solar radiation (C)</p> Signup and view all the answers

    The rate of photosynthesis remains constant regardless of light intensity.

    <p>False (B)</p> Signup and view all the answers

    Increasing the demand for assimilates in the leaves always leads to a decrease in the rate of photosynthesis.

    <p>False (B)</p> Signup and view all the answers

    What are the two critical aspects of solar radiation that directly influence crop growth?

    <p>Light intensity and light duration.</p> Signup and view all the answers

    The ______ stages of a crop are particularly sensitive to solar radiation.

    <p>reproductive and ripening</p> Signup and view all the answers

    During which stage of growth are fruit and seed crops most sensitive to water stress?

    <p>Reproductive stage (C)</p> Signup and view all the answers

    Crops with high water use efficiency are less able to cope with water stress.

    <p>False (B)</p> Signup and view all the answers

    How does nitrogen status affect cereal crop yield?

    <p>Nitrogen status influences grain yield by affecting the size and duration of canopy expansion, which in turn affects the efficiency of solar radiation capture for converting into organic compounds.</p> Signup and view all the answers

    Extremes of temperature can ______ physiological processes and inhibit plant growth.

    <p>adversely affect</p> Signup and view all the answers

    Match the following growth stages with their corresponding crop types:

    <p>Active vegetative growth = Leafy vegetables Formation and development of the storage organ or tuber = Root crops Reproductive stage = Fruit and seed crops</p> Signup and view all the answers

    Temperature is the only environmental factor that influences plant development.

    <p>False (B)</p> Signup and view all the answers

    Explain how soil temperature affects germination.

    <p>Soil temperature influences germination as it controls enzymatic reactions required for water imbibition by the seed.</p> Signup and view all the answers

    During which season is dry matter primarily distributed to the roots?

    <p>Winter (B)</p> Signup and view all the answers

    What is the primary function of storage organs like stems in plants?

    <p>To mobilize assimilates to grains, seeds, fruits, and tubers (D)</p> Signup and view all the answers

    The key to maximizing crop yield is to minimize radiation interception.

    <p>False (B)</p> Signup and view all the answers

    What is a recommended practice in areas with low rainfall to ensure crop productivity?

    <p>Choose annual crops instead of perennial crops</p> Signup and view all the answers

    Improving harvest index can lead to an increase in the __________ of important cereal crops.

    <p>yield components</p> Signup and view all the answers

    Study Notes

    Plant Physiology - Assimilate Partitioning

    • Photosynthesis and translocation occur simultaneously in green plants
    • Early plant growth utilizes photosynthetic products for vegetative structures
    • Later, products are used for storage organs (grains, fruits, tubers, seeds)
    • If photosynthetic product supply exceeds demand, it's stored in stalks and leaves, then later transported to growing parts.
    • Translocation occurs through phloem, the conducting tissue
    • Plasmodesmata, tubelike strands, connect cells and move photosynthetic products.
    • Leaves export a significant portion (70-80%) of photosynthate within 6 hours of photosynthesis
    • C₄ plants have a faster translocation rate compared to C₃ plants.
    • Efficiency of translocation in C₄ plants may be due to specialized Kranz anatomy and greater phloem amount.
    • Factors like water stress, nutrient deficiencies, or extreme temperatures can reduce translocation in plants.
    • Source organs are plant parts that produce carbohydrates (photosynthesis products) - example is leaves
    • Mature leaves are the main source of assimilates produced during current photosynthesis, supplemented by stored reserves.
    • Sink organs receive and utilize photosynthates. Examples include developing/growing organs like fruits, grains, seeds, tubers, and young leaves
    • Young leaves act as sinks as they do not produce enough food for their growth
    • The rate of photosynthesis is influenced by demand from sinks
    • Removal of tubers or inhibition of tuber growth reduces net assimilation rate
    • Removal of fruits or florets decreases net photosynthesis

    Components of Yield

    • Crop yield is the economically useful part for human or animal consumption, measured as grains or dry matter per unit land area.
    • Yield is expressed in kg/ha or metric ton/ha
    • Biological yield is total dry matter, whilst economic yield is the useful part.
    • Yield components in cereals include panicles/ears per unit area, spikelets/grains per panicle/ear, and weight per spikelet.
    • Yield = (no. of panicles/m²) * (no. of grains/panicle) * (weight/grain)
    • Yield in legumes considers pods per unit area, seeds per pod, and weight per seed.
    • Yield in tuber crops involves stems/m², tubers/stem, and average tuber weight
    • Yield in forage crops involves plants/m², shoots/plant, and weight/shoot

    Harvest Index

    • Harvest index (HI) quantifies economic yield (grain/fruit/tuber) relative to the total biomass produced
    • HI of rice is calculated as the ratio of grain weight to above-ground biomass.
    • A higher HI signifies that most assimilates are partitioned into economically important parts.

    Changes in Assimilate Partitioning

    • Assimilate partitioning changes as the plant grows.
    • Early plant growth directs assimilates to vegetative organs.
    • Following reproductive development, assimilates are channeled to fruits, seeds, tubers.
    • Soybean crop initially prioritizes leaf canopy, but later diverts more to flowers, stems and petioles (increasing proportion as flower population increases).
    • In the final stages, assimilates are channeled to the grains.
    • Crop also experiences dry matter loss from senescent leaves and stems which contribute to grain yield proportion in maturity, contributing high proportion of dry matter.

    Limiting Factors of Crop Yield

    • Several factors can limit crop yield, including water supply, nitrogen nutrition, temperature, solar radiation, plant population, and diseases/pests/weeds.

    1. Water Supply

    • Water status affects leaf size, longevity, carbohydrate assimilation, and grain-filling duration.
    • Water deficits during canopy establishment can reduce leaf size.
    • Water deficits reduce grain fill duration due to premature senescence.
    • Specific developmental periods are sensitive to moderate water stress, especially root/leafy vegetables during respective growth periods.
    • Yield depends on the quantity of transpired water.
    • Crops with high water use efficiency (transpire less, absorb more) can better withstand water stress.

    2. Nitrogen Nutrition

    • Nitrogen status affects cereal crop grain yield by influencing canopy size and duration.
    • This in turn influences the efficiency of solar radiation capture, and conversion into organic compounds.

    3. Temperature

    • Temperature affects photosynthesis and respiration rate, flowering, assimilate partitioning, leaf production and maturity.
    • Extremes inhibit plant growth
    • Plants grow faster within a favorable temperature range, provided other environmental factors like nutrients, water, and light aren't limiting.
    • Different crops/varieties require specific temperatures for optimal performance.
    • Temperature affects seed germination, water absorption, nutrient absorption and subsequent translocation and assimilation in the plant.
    • Temperature influences the partitioning of growth between shoot and root, with a cold season favoring root weight and warm season favoring shoot yield

    4. Solar Radiation

    • Biomass yield under optimal agronomic practice depends on light interception by crop canopy
    • Solar radiation affects plant growth type, food material synthesis and differentiation of tissues/organs, and maturity stages
    • Light intensity and duration are critical aspects of solar radiation
    • Photosynthesis rate increases linearly with light intensity until a saturation point is reached.
    • The reproductive and ripening stages are critical in relation to solar radiation for active photosynthesis for assimilate transport to sink organs
    • Responsiveness to irradiance is higher for plants with greater nitrogen nutrition and increased leaf area

    5. Plant Population

    • Yield components are sensitive to population density
    • Overpopulation results in low weight/plant, reducing crop yield
    • At very high densities, plants focus on above-ground growth to survive at the expense of yield components like seeds/roots

    6. Diseases, Pests, and Weeds

    • Diseases, pests, and weeds reduce nutrient/water use efficiency, thus increasing production cost
    • These factors reduce crop quality lowering their price for growers

    Conclusions and Practical Applications

    • Crop yield predominantly depends on assimilate translocation to economic parts (i.e., grains, seeds, tubers).
    • A certain portion of assimilates is lost during respiration
    • Assimilation rate decreases when the crop canopy ages
    • Mature leaves act as a primary source, supporting sink growth with current photosynthesis and stored reserves.
    • Other storage organs such as stems mobilize assimilates to grains, seeds, fruits, and tubers.
    • Regrowth in grasses after grazing depends on reserves in roots
    • Weeds' persistence may be from rhizomes/stolons for sustaining rapid regeneration
    • Improving harvest index is vital for boosting yield components in crops. Shorter stature cultivars reduce competition between stem and grains, thereby improving harvest index
    • Maximizing yield hinges on maximizing light interception
    • Crop water stress remains the primary yield limiting factor worldwide
    • In areas with limited rainfall, annual crops over perennial ones are recommended, due to their short life cycle that ends before severe droughts
    • Fertilizers should be applied strategically during critical developmental stages to improve nutrient uptake efficiency.

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    Related Documents

    Plant Physiology - LU 8 Assimilate Partitioning - 2018-19 Past Paper PDF

    Description

    Explore the processes of photosynthesis and translocation in plants through this quiz. Understand the roles of source organs, how photosynthetic products are utilized, and the differences between C₃ and C₄ plants in assimilate partitioning. Test your knowledge on the intricacies of plant growth, storage organs, and factors influencing translocation efficiency.

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