PLANT DEVELOPMENT & REPRODUCTION - CBSE International

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Commercial use of AuxinUse of auxin can be seen in diverse areas such as, methyl esters of auxin. These are to preventsprouting in potato in store houses that increases the life of potato for sale in market. Byknowing the fact that auxin plays florigenic role in dry neutral plants and promotes formationof female flower, synthetic auxin 2,4-D and NAA are used to induce flowering in litchi andpinapple. Fruit and leaf drop is prevented by auxin along with thinning of fruits that enhancesthe productivity of fruit crops. Plant productivity is also enhanced by removal of weeds fromcrop fields by use of auxin as a herbicide (Dicamba, 2,4-D). Auxin leads to root induction fromcutting and this property is very helpful in horticulture.Activity 1Aim: To study the regeneration of auxin induced adventitious roots.Material required: Auxin solution, water, etiolated bean seedlings, containers.Procedure: Ten seven days old etiolated bean-seedlings were cut in two (in the middle of thehypocotyls). Five pieces each were put in auxin/water-solution for about 2hrs. The roots andshoots were sorted in different containers (layer out with wet filter paper). The four containerswere closed and sealed light-proof. The plants were stored such for one week.Result and discussion: IAA induces adventitious roots. The substance is transported from top(leafs) to bottom (roots) by besipetal transport. Therefore we expect the adventitious roots todevelop especially on the basal location. That means developing roots at the cut of the upperpart and roots on the already existing root on the lower part of the plants. The Auxin-exposedplants probably show more adventitious roots because of the inducing effect of IAA.Look at the upper halves of the cut seedlings, most of the adventitious roots develop on thelower two third of the stem. Compared to the volume, there are astonishing many roots at thecut end at IAA treated and control-plant compared with the distribution on the rest of the sprout.This again might be due to the basipetal transport which is responsible for a higher (adventitiousroot-inducing) concentration of IAA in the lower parts of samples.Q.1. Which hormone(s) plays crucial role in cell division?Q.2. What is the role of auxin in plant development?Q.3. What precautions should be taken during such experimental setup?GibberellinIt is second group of plant growth promoting hormone. Till date approximately 136 naturallyoccurring GAs (Gibberellic acids) have been identified. But, unlike auxin (diverse group ofchemicals with similar biological properties), all GAs share similar chemical structure butrelatively few of them have intrinsic biological activity. The discovery of GA was the result ofpractical observation. During late 19 th and early 20 th century Japanese farmers were sufferingwith disease in rice plants that reduced the crop yield. Such diseased rice plants became tootall that resulted in the reduction or elimination of seed production. Japanese farmers namedit foolish seedlings or bakanae disease in Japanese. Later on, plant pathologist found thatthese symptoms in rice were induced by chemical(s) secreted by pathogenic fungus GibberellaUnit 1 Plant Development & Reproduction 12
fujikuroi that had infected the plants. Later It was isolated and crystallized by Japanese workersand named Gibberellin after the genus name of the source fungus. They named it Gibberellinor Gibberelic Acid (GA) (Figure 12). GA 3was proved to be identical with Gibberllic acid.2COOH13HO3H6CO H 2CH 3Figure 12: Structure of biologically active gibberellin (GA)Chemically, all gibberellins are tetracyclic (four rings) and contain 20 or 19 carbon atoms. Thishormone is chemically terpenoid and acidic in nature. GA is synthesized by the integratedcooperation of Plastid (assembly of 4 isoprenoid units into 20 carbon linear molecules) plastidenvelope and ER (intermediate formation) and cytosol (synthesis of backbone of GA 3). Theenvironmental conditions like photoperiod, temperature can alter the level of active GA andits level in plants. Unlike Auxin, it is regulated by itself at genetic level by negative regulationof enzyme required for GA synthesis through feedback mechanism.The GA shows following physiological responses and roles in plants:GA can overcome the problem of rosette or dwarf plant by stimulating stem growth. Thisphenomenon is known as bolting (Figure 13).Boiled shoolRosette leavesFigure 13: The effect of gibberellin showing bolting in a rosette plant in Arabidopsis. (A) Anuntreated plant (Control) (B) GA treated plant showing boltingIt also helps in shifting of juvenile to adult phase. GA influences the floral initiation andsex determination. Floral initiation in monocot (Zea mays) by GAs is suppressive for stamendevelopment and resulting in female or pistillate flower but in dicot flowers like cucumber,hemp and spinach, GAs promote formation of male flower and suppress female flower. GAindirectly promotes male character by promoting pollen development and tube growth. GApromotes fruit set in Pyrus and parthenocarpy in grapes (Vitis sp.). In grapes it also reduces thefungal infections. GA promotes seed development and germination. This response is promotedby GA by inducing the expression of hydrolytic α-amalyase enzyme in living aleurone layercells of seed.Unit 1 Plant Development & Reproduction 13
Page 3: The CBSE-International is grateful
Page 6 and 7: PrefaceEducation plays the most imp
Page 8 and 9: AcknowledgementsAdvisoryShri Vineet
Page 10 and 11: 2. Cell enlargement: In this phase,
Page 12 and 13: Auxanometer(Gr. auxain, “to grow
Page 14 and 15: with simple cell/organism like bact
Page 16 and 17: Primary and Secondary growthin a tw
Page 18 and 19: activity, such as Indol-3-ethanol,
Page 22 and 23: Commercial Application of GA1. GAs
Page 24 and 25: ABA (Abscisic Acid) Savoir from adv
Page 26 and 27: OHEthylene is also involved in the
Page 28: Salicylic acidIt is naturally occur
Page 31 and 32: carried out mainly by two types of
Page 33 and 34: conditions are favorable and ample
Page 35 and 36: Figure 23: Flower showing the male
Page 37 and 38: What would be theploidy of the cell
Page 39 and 40: Activity 6Aim: To study the pollen
Page 41 and 42: Megasporogenesis: The process of fo
Page 43 and 44: synchronized. Either the pollen is
Page 45 and 46: Pollination by water is quite rare
Page 47 and 48: on the stigma. The pistil has the a
Page 49 and 50: Antipodal cellPolar nuclei(n)Female
Page 51 and 52: called coleorrhiza. The portion of
Page 54 and 55: Activity 8Observe some flowers of t
Page 56 and 57: Unlike polyembryony, the apomixis i
Page 58 and 59: of vascular plants (Dicots, gymnosp
Page 60 and 61: two polar nuclei (the second polar
Page 62 and 63: Q.4. Discuss the photoperiodism and

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