| The seedling is a critical stage in a plant's life-cycle during which seed reserves are utilized for the seedling to survive until it becomes autotrophic. Because of the importance of the process, the mobilization of reserves is regulated at many points and levels and this regulation is a significant aspect to study. Fenugreek (Trigonella foenum-graecum L.) seedlings represent an unique opportunity to study regulation of carbohydrate mobilization because three different carbohydrates (galactomannans, soluble sugars, and starch) are utilized during establishment.; Within the seeds of fenugreek, the major carbohydrate reserve is the galactomannans in the endosperm. Endo-{dollar}beta{dollar}-mannanase, an enzyme required to mobilize this reserve, increased in activity in the axis (hypocotyl and radicle), cotyledons, and endosperm and was correlated to fresh weight decreases in the endosperm. Isozyme analysis showed 4, 8 and 5 isozymes in the axis, cotyledons, and endosperm. respectively. An isozyme survey of many angiospermous and gymnospermous seeds in both the dry and imbibed states and of the vegetative parts of flowering alfalfa demonstrated the ubiquity of the enzyme and corroborated a probable function other than strictly mannan reserve mobilization. Endo-{dollar}beta{dollar}-mannanase activity was partially regulated by sugar, osmotic stress, and ABA.; The amount of galactosyl-sucrose sugars decreased and sucrose increased significantly in the first 24 h of imbibition in all three tissues as expected with post-germinative mobilization of reserves. In the endosperms, as expected with hydrolysis of the galactomannan, both mannose and galactose content increased. Quantities of adenosine diphosphoglucose (ADPG) increased in the cotyledons with time, suggesting that ADPG pyrophosphorylase was not the rate-limiting step in starch synthesis.; The osmotic stress that the influx of sugars from the endosperm created was eased by a transient starch accumulation. Treatments which resulted in the accumulation of different quantities of starch were used to attempt to determine the level at which starch synthesis was primarily regulated. The amounts of ADPG pyrophosphorylase transcript corresponded to the starch which accumulated with treatment. Starch phosphorylase, an enzyme which can act in either a synthetic or degradative capacity, was present at all times in at least 2 forms. Alpha-amylase activity was consistently low for both the axis and cotyledon but amylase activity and protein increased by about six times in the cotyledons. The timing of this increase with relation to starch accumulation suggested {dollar}beta{dollar}-amylase was serving a function beyond degradation of starch. |
