The role of plant growth regulators in the development and germination of the desiccation-sensitive (recalcitrant) seeds of Avicennia marina

Abstract

The contents of the cytokinins zeatin (Z), zeatin riboside (ZR), and isopentenyladenine (IPA), the combined contents of gibberellins1 + 3 (GA), and the contents of indoleacetic acid (IAA) and abscisic acid (ABA) were measured during the development of the desiccation-sensitive seeds of Avicennia marina (Forssk.) Vierh. During the stage of histodifferentiation the amounts of these plant growth regulators (PGRs) were measured on whole fruits. During the phase of seed growth and reserve accumulation measurements were made on the embryonic axis, cotyledons and pericarp separately. Patterns in the amounts of PGRs present during histodifferentiation were similar to those reported for desiccation-tolerant seeds and it suggested that this process is under similar ‘hormonal’ control in A. marina as in orthodox seeds. Very high contents of cytokinins, particularly ZR, were present in both axes and cotyledons during reserve accumulation. This is thought to be related to the nature of the reserves accumulated (soluble sugars), rather than to the phenomenon of desiccation sensitivity. With the exception of ABA, embryonic contents of PGRs were relatively high at seed shedding, consistent with the rapid germination of this highly recalcitrant seed. ABA contents in the embryo were low during reserve accumulation, but concentrations in the pericarp increased throughout this development stage. ABA in the perticap could act to prevent precocious germination. The low concentrations of ABA in the embryo could be related to the desiccation-sensitivity of the seeds of A. marina.

Germinação e armazenamento de sementes de uvaia (Eugenia pyriformis Camb.) – Myrtaceae

“…Não suportam o armazenamento com baixa umidade sem perder sua viabilidade. O período máximo de armazenamento varia entre as espécies recalcitrantes e está relacionado com a germinação (Ferrant et al, 1993b).…”

Changes in endogenous indole-3-acetic acid and some biochemical parameters during seed development in Camellia sinensis (L.) O. Kuntze

“…The re cal ci trant seeds in gen eral, char ac ter is ti cally re main met a bol i cally ac tive on shed ding and con se quently ger mi nate im me di ately af ter abscission. Gen er ally, the pro cess of ger mi nation be gins even be fore shed ding (Berjak et al 1989) and both IAA and cytokinins play a cru cial role dur ing the on set of ger mi na tion in the re cal citrant seed spe cies like Avicennia ma rina (Farrant et al 1993). …”

“…Rather, the level con tin ued to rise and at tained the max i mum at late em bryo mat u ra tion stage. Per sistently high level of free IAA even at full ma tu rity can prob a bly be ex plained by the fact that as in most re cal ci trant seeds, the tea em bryos even with high crit i cal mois ture con tent of about 30.6 % prior to seed shed ding (Bhattacharya et al 2002) had the po ten tial to ger mi nate up to the ex tent of 100% and this high lev els of free IAA were prob a bly re quired for the ini ti a tion of the ger mi na tion pro cess (Farrant et al 1993) and for the IAA reg u lated me tab olism in the ger mi nat ing seeds (Co hen and Bandurski 1989, Bialek and Co hen 1989). The sig nif icance of greater in crease in IAA dur ing em bryo mat u ra tion phase of tea by 2-3 or ders of mag ni tude as com pared to most re ports could be due to two pos si bil i ties: firstly re serve mo bi li za tion in the coty le dons by IAA as in pea (Hirasawa 1989) and secondly stim u la tion of cot y le don ary pho to syn the sis as in many veg e ta tive tis sues (Brenner 1987). Comparatively, the level of IAA was very high in the fruit wall dur ing the early stages (5-6) as compared to em bryo and seed coat.…”

Dormancy and germination in Stachys germanica L. subsp. bithynica (Boiss.) Bhattacharjee seeds: Effects of short-time moist chilling and plant growth regulators

“…Cytokinins are present in relatively high concentrations, e.g., in Table 2 Final germination (%) and mean germination times ( the recalcitrant seeds of Citrus spp. (Elotmani et al, 1995), Avicennia marina (Farrant et al, 1993), and several other viviparous species of mangroves (Farnsworth, 1997), indicating that they may be involved in maintaining continuous cellular activity. In addition, cytokinins may also help halophytes to overcome salt-induced inhibition of germination (Gul and Weber, 1998).…”