Plant Growth and Development PDF

2 1518 MODERN’S abc + OF B|OLOGY—Xl ADDITIONAL USEFUL INFORMATIONS ABOUT GROWTH AND DEVELOPMENT FOR COMPETITIVE EXAMINATIONS I The arithmetic growth of ro...

2 1518 MODERN’S abc + OF B|OLOGY—Xl ADDITIONAL USEFUL INFORMATIONS ABOUT GROWTH AND DEVELOPMENT FOR COMPETITIVE EXAMINATIONS I The arithmetic growth of root can be pat as Lt = Lo + rt where Lo is length at zero time, Lt at time t and r is growth rate. I Crescograph is used fin recording plant growth in seconds. I Strasburger studied growth in root by marking it at equal intervals with India inlc. I In growth, anabolic processes dominate over catabolic processes and therefore growth is thefinal product egfsnccessfnl metabolism. I The abrupt change from juvenile to adult phase is called heteroblastic development. I The dijjferent aspects or appearances of plants in different seasons of a year is called phenology. I Part of the year, when maximum growth occurs is called growing season. I The automatic or Pfejjfer’s anxanometer is an improvement over the arc anxanorneter. It can register total growth, rate of growth at specific time and overall pattern of growth. I Negative growth is the term sometimes used for senescence. PLANT GROYVTH REGULATORS (PGR) He noticed that when a unilateral source of light was Or given, the coleoptile would bend towards light. Darwin PHYTOHORINIONES was of the view that tip contained a substance which was able to perceive the light stimulus. He believed that The presence of growth regulating chemicals in substance was transmitted to lower portion which caused plants was first suggested by Sachs in latter half of bending. He further demonstrated that a decapitated nineteenth century. The plant hormones act as messenger coleoptile or a coleoptile which was covered with opaque substances for growth regulation. These hormones tinfoil cap failed to respond to unilateral source of light are organic substances which are required in small (Fig. 15). He further noticed that curvature occurred when quantities at low concentrations and their sites of action the seedling was buried in fine black sand excepting the and synthesis are usually different. Most of the plant extreme tip of the coleoptile. hormones represent a broad action spectrum and thus Boysen-Jensen (1910-13) noticed that ability to a single hormone may influence several processes. Plant growth regulators include both endogenous show phototropic response was lost, if the tip was decapitated. However, if the removed tip is again and synthetic compounds. A particular hormone may placed on the stump, bending activity was recovered. promote certain physiological processes, inhibit some This phototropic response was exhibited even in the others and not affect many others. Developmental case when a gelatin piece was kept between the stump processes are regulated by growth regulators acting and the decapitated tip (Fig. 16). Boysen-]ensen further synergistically (co-operative and beneficial) or found that if transverse slit was made in the coleoptile antagonistically (opposite) with one another. Following on the darker side and a mica piece was inserted in the categories of growth regulators will be discussed in slit, no phototropic response occurred. As compared to this chapter : this, phototropic response took place if the slit and mica 1. Auxins 2. Gibberellins 3. Cytokinins 4. Ethylene piece were inserted on the illuminated side. 5. Abscisic acid. DARK SIDE cunvarune N0 RESPONSE M TOWARDS LIGHT AFTER THE TIP |s covsneo Auxins are one of the most important group of WITH TIN FOIL plant hormones. Auxins were the first to be identified ILLUMINATED S|DE ‘ NO RESPONSE AFTER as growth hormones. LAA (Indole acetic acid) is the - '=-. REMOVAL OF TIP principal naturally occuring auxin found in all plants including fungi. The compounds which can be converted '.'--':Z:-- 1.‘ I I I. ~ into auxins are called auxin precursors. The compounds I ::‘: which retard or stop the activity of auxins are called LIGHT I" ‘I —-—-—D I anti-auxins. The type of auxins which can be easily ————D extracted are known as free auxins. The type of auxins -—ZD I —i-P which are difficult to extract and require the organic ———D- solvents for extraction are called bound auxins. Free -—ZII ~ ' A _ form of auxins is considered to be active and bound form of auxins is inactive in growth. Both the forms are fotmd in dynamic equilibrium. The first indication -- I11: I I_'.. about the existence of auxins was marked in work of DAHw|N (1830) HORMONE ABSENT Charles Darwin (1880), who was studying the bending of the coleoptile of canary grass (Phalaris) towards light. Fig. 15. Work of Darwin (1880). PLANT GROWTH AND DEVELOPMENT TIP REPLACED °s.s;ss.1.P GELATIN BLOCK GROWTH TAKES PLACE WHEN MICA IS INSERTED ON ILLUMINATED SIDE GROWTH TAKES PLACE no onown-1 WHEN anon IS INSERTED ON DARK COLEOPTILE LEAF " _""‘ "4‘“ "4'“;,-,I.'uv\.>0v\.v-‘Q q-1.»i-.1 -rt.-urn‘:-4'r~‘-" "w' PRIMARY Q! FIOOT ,\ B Fig. 18. A. Oat coleoptile B. L.S. of the same showing BOYSEN JENSEN (1910-1913) HORMONE ABSENT coleoptile sheath enclosing primary leaves. GROWTH Fig. 16. Work of Boysen-Jensen (1910-13). CURVATURE AN AGAR BLOCK IS TAKES PLACE Paal (1918) demonstrated that when the decapitated PLACED ECCENTRICALLY tip was replaced on the cut end eccentrically, more growth resulted on that side which cause bending even though this was done in complete darkness (Fig. 17). DECAPITATED TIP REPLACED ECCENTRI- EDD CALLY GROWTH TAKES - PLACE ' _. TIP -I.'-‘i-i ‘F.'E = '5 r. Fig. 19. Went's isolating auxin experiment. DARK ISOLATION AND MOLECULAR STRUCTURE ______.1. PAAL(1e14-1919) Kogl (1931) and Thimann (1935) isolated the auxins Fig. 17. Work of Paal (1914-19). and studied their chemical nature. Kogl succeeded in isolating auxin- a (auxentriolic acid, C18H32O5) from Final evidence was provided by Went in 1928 that urine of a pathological Dutch patient. Kogl et. al. (1934) some substance is responsible for tmilateral growth isolated another auxin called auxin-b (auxenolonic acid, and this substance is supplied by tip. Went placed C18H30O4) from corn germ oil. They isolated another decapitated Avena coleoptile tips over thin blocks of auxin from hiunan urine called heteroauxin (indole- agar-agar. Agar-agar is a polysaccharide, which attains 3-acetic acid, IAA, CmI—I9O2N).Thimann isolated IAA a gelatin-like consistency when dissolved in water and from the culture filtrate of Rhizopus sninns. Few other allowed to cool. Agar block was placed on inert material auxins are Indole butyric acid, Indole-3-Pyruvic acid, like glass. Then he cut the agar block into small cubes Phenyl acetic acid, Indole butyric acid, Naphthalene acetic acid (NAA), 2-4 dichlorophenoxy acetic acid etc. (Fig. 18). He discarded the tips and placed the agar (Fig. 20). The usual site of auxin synthesis are meristems. cubes eccentrically on coleoptile stumps for two hours in It is found in human urine, particularly in persons dark. He found that curvature was produced. He called suffering from pellagra (niacin or nicotinic acid the substance as auxin (Gk : auxein---to grow). Went deficiency). Role of IAA in human being is not clearly concluded that "no growth can occur without auxin”. understood yet. 15"" MODERN’S abc + OF BIOLOGY—Xl I“ ‘ I 600 0 PLASTICITY -o N N N :|:oI H H INDOLE 3-ACETIC ACID INDOLE 3-PFIOPIONIC ACID (ii Iii! LA Uc1-1,c1-121:1-1,0001-1 oH2coo|-1 hGpFIOrWTH 8 / N-I5 INDOLE 3-BUTYFIIC ACID NAPHTHALE_NE ACETIC ACID FIcnvPLAESTTvs [iii] (Iv) O C c1-1, 0 104 10"“ 10 ’©:q H2600‘-i ‘ Z - f)=CD —s—oI-|,coo|-| nu. CONCENTRATION mg;‘LITFtE 0| ca,’ 2-4 DICHLOROPHENOXY cARB°xY'“E"HY'- DIMEFHYL Fig. 22. A comparison of the effects of IAA on growth and ACETIE) ACID (vi) DITHIO CARBAMATE cell wall plasticity in Avena coleoptiles. Fig. 210. Structure of IAA and some synthetic auxins. 4. Apical dominance. in many plants, it is observed that removal of terminal bud leads to prompt growth of FUNCTIONS OF IAA (PHYSIOLOGICAL EFFECTS) one or many lower buds. The auxins in apical bud inhibit The role of IAA to humans is not known. Auxins the development of lateral buds and the phenomenon is perform many ftmctions and physiological activities in called apical dominance. Recent investigations support plants.Few important are discussed below : the view that auxins induce the fonnation of the ethylene 1. Cell division. Auxins initiate as well as promote which acts as inhibitor for lateral buds. The process cell division in tissues like cambium (Fig. 21). In tissue can be reversed if LAA is applied to decapitated apex. culture, by addition of hormones like auxins, callus is 5. Prevention ofAbscission layer. Another inhibitory formed. It is due to vigorous division in parenchymatous effect of auxins is on abscission of leaves and fruits which cells. The reactivation of cambium in favourable season leads to leaf fall and fruit drop (Fig. 25). Leaves separate is triggered by auxins, migration from developing shoot from the stem following changes in the chemical and buds. The effect of auxin is particularly important in physical properties of cells in abscission zone, a group secondary growth of stem and differentiation of xylem of cells at the base of petiole. The concentration of IAA and phloem tissues. i.n cells near or within the abscission zone appears to bear some relation to the abscission zone. 300 ‘ The effects of auxins on plant development described WITH above give only a partial view of what actually occurs. INDOLE ACETIC ACID 0.1 mg,-‘I The effects discussed are based on the assumption that IAA is the sole phytohormone involved. § USES OF AUXINS 1. Eradication of weeds (Fig. 23). The roots are WEGHT mg WITHOUT IN DOLE extremely sensitive to auxins. High concentration ACETIC ACID of auxins like 2, 4-D (2,4 dichlorophenoxy acetic acid) 2,4,5—T (2,4, 5 trichlorophenoxy acetic acid) ‘I Q 4 8 WEEKS Fig. 21. Callus growth with and without the SPRAY II addition of IAA. 2. Cell elongation. Long ago, it was noticed that /1 » II I auxins stimulates cell elongation. Auxin is thought to cause the walls to become plastic and due to endosmosis, cell elongates. [AA effect on growth is directly related to its effect on cell wall is illustrated by American physiologist R. Cleand (1967) (Fig. 22). I\ 3. Root formation. Auxin stimulates the formation of new roots. However, their application retards the root BROADLEAVED WEED U WHEAT OR OTHER GRASS NOT growth. Thus cell division initiated by auxins leads to KILLED BY 2.4-D SPRAY INJURED BY 2,4»-D SPRAY the formation of adventitious and lateral roots in plants. Fig. 23. Destruction of weeds by 2,4-D. PLANT GROWTH AND DEVELOPMENT overstimulate growth pI‘01T\Oting activities of the cells of in vegetative propagation. Auxins like IAA, IBA, NAA, the root. As a result roots get distorted, sieve tubes get 2,4-D when applied in low concentrations from 10 to blocked. Disturbance in cell division also occurs. 1000 parts per million on cuttings initiate adventitious This leads to decay of roots and finally plant is root formation. killed. 2,4-D is used to destroy broad leaved 3. Flower initiation. Auxins normally inhibit dicots (mostly weeds). However auxins like 2,4-D and flowering. However in litchi and pineapple (Anmms 2,4,5-T are non-toxic to narrow leaved plants i.e., safivus) auxins like 2,4-D and NAA have been found to monocots. Auxins are being used as weedicides mainly promote flowering. l/Vhen auxins in dilute concentrations due to : are sprayed on pineapple plants, uniform flowering (a) They are economical, because they act at very occurs. However, in lettuce auxins help in delaying low concentrations. the flowering. By treating the lettuce with auxins, the (b) Due to their selective herbicidal nature. plants are kept vegetative for a longer time. (c) Toxic residues of auxins disappear from soil 4. Production of parthenocarpic fruits. The very soon. conversion of ovary into fruit had been believed mainly (d) Auxins at low concentrations are not harmful due to the activity of auxins. If treated with auxins, to living beings. plants have been found to develop fruits even in the 2. Root initiation. Thimann st. al. have demonstrated absence of pollination and seeds. Fruits such developed that root forming substance and auxins are identical. are seedless (Fig. 24), hence called parthenocarpic. Such Application of auxins activates root initials. Rapid seedless fruits are Obtained by treating the flowers with adventitious root formation is absolutely essential in low concentration of auxins. cuttings for their successful development into new plants ad £@ NO e - POLLINATIO 1 ' B FLOWER UNPOLLINATED c OFF DROPS \_ 5_-. / APPLICATION o OF AUXIN STYLE PASTE FOFIM L if ’ In "*J@ D - LLINATIO. \ _ '1 A UNPOLLINATED FLOWER CLUSTER OF FLOWERS ON TOMATO E INITIATION OF FRUIT DEVELOPMENT Fig. 24. Development of seedless fruit by auxin. AGAH BLOCK CONTAINING AUXI.-‘P R... VASCUl_AFl BUNDLE OF. PETIOLE. o_-.-.-.' ¢, P‘.| __ ' - 0.. _ - 1. 2'..' , in in -Fit‘.-.; _ -::E:1_ ‘7»;___.;_'7a*.-‘i'm '--. -_-i. _-G,» ~--:.'.'.-__l\_m¢. - -i 9:-it-:11: -|'.’r¢'-?.v~.¢,.!‘;_... -' =.-:--:-:'- "'1-'6»-§=:>"~' - :55. - -'-"'5'-'-“' i\'li~'?-*1?" * I ,- -:. --.1225_ ii:-:5. -. -- _ _, 'I ,‘.\f.~}\'~?‘," \ \_/ \ a- eh. 1:-' = =...-.;; " '5" J-I’ _»'.._. f’."-1 -ll} F? Ls V.I".1'. ‘___ ‘ I.-.*f-‘Sari: I -l 5. _ l tr _ _.|| " -‘re. 1 1; l. 1' V, _- _-R":.,_____J.4?!‘ I‘. '-.;_=J=9 5?»? 5-st- I ___._; I I W("" '_;-1.1..61. I ’ - the l'¢r.=. =---. -q-‘=§- r- -' _..F I 535‘ 1 a I UCTION wrm SHORT DAYS VEGETATIVE QQQKLEBUH RETURNED TO LONG DAY ORIGINALLY VEGETATIVE COCKLEBUR P|_ANT AND GRAI-_l'ED TO PLANT FLOWERS AS A PLANT FLOWERS VEGETATIVE PLANT RESULT OF GRAFT Fig. 40. The flowering stimulus may be transmitted from plant to plant across a graft union. PLANT GROWTH AND DEVELOPMENT SHORT DAYS LONG DAYS ,- Ii" e§.i3i4*_sil;*,-at. -if -_ NOT SUBJECTED TO COLD , agrlrk pi. -'7.‘. fie,. F11-1%? r-E‘