Background: Seed recalcitrance is a major problem associated with many tropical plants, limiting their natural regeneration. Vateria indica L. is a vulnerable and endemic tree species in South-Western Ghats of India, which is also recalcitrant. ABA and gibberellins are the most important plant hormones required for seed germination. It is the balance between ABA and GA which is responsible for desiccation tolerance in orthodox seeds. Exogenous hormones pretreatment has been also reported to influence seed germination. But such studies had been sparsely done in the case of recalcitrant seeds. This study aims to find out whether GA/ABA antagonism in recalcitrant plants is operating in the same way, like that in the orthodox seeds.Methods: The effect of the exogenous pre-soaking application of phytohormones viz. GA3 and ABA individually as well as their combinations on seed germination and growth of Vateria indica L. were carried out in the present work. The seeds were collected from April to July 2018 and the experiment was designed at Post Graduate and Research Department of Botany, Government College for Women, Thiruvananthapuram. When different concentrations of each phytohormone were externally given to the seeds, ABA reduced the germination and growth in almost all the concentrations. But GA3 gave better results. When combinations of GA3 and ABA were used, germination was poor in the sample where ABA was more than GA3, But in samples with same concentrations of both the hormones and with more GA3 gave better results. Result: This study clearly showed that GA3 when given externally along with ABA, might have affected the endogenous ABA in this recalcitrant seed and suppressed its retarding effect. Thus ABA/GA antagonism is working out, here, in the same way as in orthodox seeds. Since the germination of recalcitrant seeds is a less investigated area, the present study will form a basis and a lot more for further such studies.
Vateria indica L. is an endemic arborescent recalcitrant tree species, native to the South-Western-Ghats of India. The natural regeneration process of the species is hindered by many factors including seed recalcitrance. Recently the species has been categorised as vulnerable since the population is fragmented and rapidly declining. Seed development is a highly complicated process which involves the interaction between phytohormones which regulate the process at different stages of morphogenesis. The orthodox seed development is marked by three distinct stages such as histodifferentiation, reserve accumulation and drying but in recalcitrant seeds, drying phase is absent. Recalcitrant seeds show marked differences from orthodox seeds in development. The onset of different stages is marked by a definite peaking and lowering of phytohormones and the hormonal pattern varies in orthodox and recalcitrant seeds. The present study was conducted to understand the interplay of phytohormones during embryogeny and the following natural embryo desiccation in the recalcitrant seeds of Vateria indica L. The present study revealed that the embryogeny and embryo drying in the recalcitrant seeds of Vateria indica L. shows a striking dissimilarity with the characteristic pattern of hormonal flux in orthodox seeds.
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