Control Processes in Other Seeds

Transversely cut apical (embryoless) half-grains of rice respond to GA and produce a-amylase and proteinase water-imbibed controls produce neither enzyme [87, 90]. In embryoless grains of IR8 rice, proteinase production precedes that of the amylase by 2.5 days (cf. barley). The embryos of normal varieties of rice appear to produce sufficient GA to induce the production of hydrolases in the germinated grain, but certain dwarf rice lines have a low endogenous GA level, and hence lower a-amylase and proteinase production [90]. 

Knowledge concerning the control of reserve food mobilization in seeds other than cereals is limited. The reason for this may be because no system as 

But before discussing these aspects some questions should be considered are the enzymes which participate in food mobilization present in the dry seed, requiring only hydration and possibly activation, or alternatively, are they synthesized during germination and growth  

Most of the evidence suggests that the enzymes are newly synthesized, though in the majority of cases rigorous proof is unavailable. Enzyme development in a number of seeds is prevented by inhibitors of protein and/or RNA synthesis. For example, dipeptidase and isocitrate lyase development in Cucurbita maxima [92, 105] are suppressed by protein synthesis inhibitors, while actinomycin D, which inhibits some DNA-dependent RNA synthesis, prevents the increase in lipase and isocitrate lyase of castor beans [14, 77]. Studies with inhibitors can be criticized on several grounds especially since these chemicals may have previously unsuspected side effects. But more satisfactory evidence of the kind known for barley aleurone layers has been found in some seeds. De novo synthesis of isocitrate lyase in cotyledons of Citrullus vulgaris (watermelon) [52] and of endopeptidase in mung bean [21 a] have been shown to occur by means of density-labelling experiments with D2O. 

Nevertheless, there are also reports, some of which are again based on the use of inhibitors, that certain enzymes involved in mobilization are not newly synthesized. The compound azetidine-2-carboxylic acid, an analogue of proline, does not stop isocitrate lyase increase in Cucurbita pepo or Cucumis sativus and it is therefore presumed that the enzyme existed in an inactive form before the chemical was applied [98]. Secondly, in some cases mobilization enzymes can be extracted from dry seeds (i.e. before germination) such as acid lipase in castor bean (see Fig. 6.8 [84]). Finally, it is thought that in some seeds trypsin- 

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By far the most work on the control of enzymes responsible for the mobilization of stored reserves has been carried out on cereal grains and some of the possible reasons for the preferential use of this material should become clear in this chapter. Discussion of this topic inevitably involves a consideration of the effects of plant hormones on cell metabolism and, more specifically, of their actions in non-growing storage tissue. The reason for this is that in the best-understood system—the cereal grain—mobilization of food reserves is quite clearly under hormonal control. The major part of this chapter is therefore devoted to regulation in these grains, especially barley and wheat, but we conclude with an account of control processes in other seeds. 

Item d implies that in terms of the Hansch model of Equation 1, partitioning STEP 1 is the primary rate-controlling process characterizing the herbicidal action of the 3-TFMS compounds on Wild Mustard in the presence of Tween 80. Since all the other Hansch relationships in Table XI include fairly significant pa contributions, partitioning as well as other rate processes (possibly more intimately connected with the receptor site within the plant or seed) must be involved in determining overall herbicidal activity in these latter cases. One may speculate that the anomalous observations (a-c) above are the direct consequence of (d)—the lack of Hammett a dependence. If the pa term in the Hansch equation does indeed reflect rate or equilibrium events occurring at or near the herbicidal site of action within the plant or seed (as is often assumed but not... 

PVDF exhibits a complex crystalline polymorphism, which cannot be found in other known synthetic polymers. There are a total of four distinct crystalline forms alpha, beta, gamma, and delta. These are present in different proportions in the material, depending on a variety of factors that affect the development of the crystalline structure, such as pressure, intensity of the electric field, controlled melt crystallization, precipitation from different solvents, or seeding crystallization (e.g., surfactants). The alpha and beta forms are most common in practical situations. Generally, the alpha form is generated in normal melt processing the beta form develops under mechanical deformation of melt-fabricated specimens. The gamma form arises under special circumstances, and the delta form is obtained by distortion of... 

In cases in which the product of a chemical reaction or salt formation is insoluble, nucleation events and precipitation may start instantaneously. These events can be difficult to control, but nevertheless one should investigate the possibility of designing an addition-controlled process—for example, by adding the reaction partner slowly— which may be coupled with appropriate seeding once supersaturation is reached. Scale-up in this area is generally difficult, and the addition mode (e.g., using spray balls or other devices to optimize the distribution of the reactant in the crystallization vessel) plays an important role. For details on precipitation, refer to the work of Sohnel and Garside. ... 

In a number of processes, including the induction of a-amylase in barley aleurone cells, the control of stem elongation and the dormancy of apical buds and seeds, ABA has the ability to counteract the specific effects of GA [30]. In other processes such as stomatal closure, the action of ABA is independent of GA [87]. 

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