Influence of Endogenous Cytokinins on Reverse Mobilization in Cotyledons of Cicer arietinum L

Abstract

The embryonic axis plays an essential role in the mobilization of the main reserves of the cotyledons of seeds of Cicer arietinum L. cv Castellana. This control by the axis of the metabolism of the storage products of the cotyledons largely takes place through the cytokinins, which are transported from the embryonic axis to the cotyledons where the mobilization of reserves begins. The principal regulatory role of the endogenous cytokinins concerns the metabolism of carbohydrates and proteins; there is less influence on lipid metabolism. However, each cytokinin seems to have a different role in the mobilization processes. The glucosides, glucosyl zeatin riboside, and glucosyl zeatin act only as storage forms of the hormones. Zeatin riboside affects mainly the mobilization of carbohydrates and has less effect on protein mobilization. Zeatin regulates both the mobilization of carbohydrates and that of proteins and is more marked in the latter case.possibility that an endogenous hormone might be involved (3).Numerous workers have confirmed the role of cytokinins in reserve mobilization in cotyledons from dicotyledoneous seeds (9, 17); however, in most studies the endogenous level of these hormones have not been taken into account, and the application of endogenous hormone could alter the response.The aim of the present work was to provide a clearer idea of the role of cytokinins in reserve mobilization, carrying out all studies after reproducing the endogenous level of cytokinins. To do so we used chick-pea seeds from which the embryonic axis had been removed, so that we knew that there would be no detectable cytokinins (16). Then, by reproducing the endogenous levels ofthe different cytokinins present under normal conditions one can gain a clear idea of the role played by each of these substances in reserve mobilization.Most research on the control of reserve mobilization has been conducted in cereals (3,31). This is possibly due to the difficulty of isolating component tissues and organs of other species for investigation, a process which is straightforward with cereal grains as a result of the spatial separation of the different tissues.Reserve mobilization in cereal seeds appears to be controlled directly by the embryo, via the production of gibberellines which initiate the synthesis and secretion of hydrolytic enzymes from the aleurone layer into the endosperm (31).In dicotyledoneous plants, the regulation of food reserve mobilization is less well understood (1 1) and many conflicting results exist in the literature concerning the role ofthe embryo or embryonic axis in the breakdown of seed reserves (3,22,26).Stimulated, no doubt, by the elucidation of the mechanism in cereals, several attemps have been made to demonstrate that a factor from the embryo or axis is also implicated in other seeds. This has been approached in two ways. First, the promotive capacity of extracts or diffusates of embryos and axes has been investigated; second, it has been argued that if a known hormone such as gibberellin or c...

Endogenous Hormone Variations in Annual Wild Cicer Species

“…Our results are in agreement with reports on cultivated chickpea (Munoz et al 1990;Babiano 1996, 1997;Turnbull et al 1997;Emery et al 1998;Hartung et al 2002). On the other hand, there were little different levels in hormones due to the fact that they have only studied cultivated chickpeas.…”

“…He reported that IAA approximately ranged from 200 pmol g À1 fresh weight in dwarf pea genotype to 800 pmol g À1 fresh weight in slender genotypes. Munoz et al (1990) found about 200-1000 ng Z per excised cotyledon in chickpea. It was pointed out that zeatin content in buds of chickpea changed little in the first 2 h (about 20 pmol g À1 FW) after shoot decapitation, but significantly increased after 6 h (more than 35 pmol g À1 FW) (Turnbull et al 1997).…”

“…So far evaluations of wild Cicer species for useful traits have provided useful data. However, relatively little is known about endogenous plant hormones in chickpea (Munoz et al 1990;Iglesias and Babiano 1996;Iglesias and Babiano 1997;Turnbull et al 1997;Emery et al 1998;Hartung et al 2002). Moreover, these studies conducted on endogenous plant hormones have been detected in cultivated chickpea.…”

Developmental stage as a possible factor affecting cytokinin content and cytokinin dehydrogenase activity in Pinus sylvestris

“…Current work shows that, apart from results obtained in seeds in which Z predominate over other CKs, iP and iPR were present in a majority in P. sylvestris juvenile tissues similarly to P. radiata (Valdés et al 2002, 2003, Zhang et al 2003. The occurrence of Z as the most abundant cytokinin in mature seeds of P. sylvestris was also found in P. pinea cotyledons isolated from germinating embryos (Valdés et al 2001), and it could allude to its involvement in the protein and sugar catabolism necessary for the newseedling growth, as it similarly happens in angiosperms (Muñoz et al 1990). DHZ and its riboside were hardly detectable in the same material, possibly because the process of hypocotyl thickening is under control of iP and Z-type cytokinins, but not DHZ (Lexa et al 2003).…”

Comparison of some endogenous hormone levels in different parts of chickpea (Cicer arietinum L.)

“…But, hormonal status of cultivated chickpea is little known and studies were mainly conducted on one or two normal leaf type chickpea (Munoz et al 1990;Iglesias and Babiano 1996;Turnbull et al 1997;Iglesias and Babiano 1997;Emery et al 1998;Hartung et al 2002). Davies (1995b) showed that the concentration of IAA was related to height of pea (Pisum sativum L.).…”