Aleurone layer development

Ogawa, M., Tanaka, K., and Kasai, Z., 1979, Accumulation of phosphorus, magnesium, and potassium in developing rice grains Followed by electron microprobe X-ray analysis focusing on the aleurone layer. Plant Cell Physiol. 20 19-27. 

A range of methods have been described in the literature, and we shall consider them in the following order (1) the methods developed at the Food Research Institute-Norwich (FRIN), to isolate cell walls from a range of vegetables and fruits (runner beans, potatoes, cabbage and apples), cereals (oats, wheat and rye) and cereal products (wheat bran and rye biscuits), and lignified tissues (parchment layers of runner bean pods) (2) the special techniques, which may include wet sieving steps, used for the isolation of cell walls from potatoes, wheat endosperm, and wheat and barley aleurone layers (3) alternative methods for the isolation of cell walls from starch and protein-rich products (rice) and (4) methods used for the isolation of cell walls from suspension-cultured tissues. 

The function of these ABA-induced proteins remains unclear. Since the a-amylase inhibitor is also synthesized during seed development, it is likely to play a mop-up role in getting rid of unwanted a-amylase activity [15,22]. Some of these ABA proteins may be related to a plant s tolerance to water stress, yet a definite proof is still lacking. In barley aleurone layers, some of these proteins could be... 

Sussex IM (1972) Somatic embryos in long-term carrot tissue cultures Histology, cytology, and development. Phytomorphology 22 50-59 Taiz L, Jones RL (1970) Gibberellic acid, -1,3-glucanase and the cell walls of barley aleurone layers. Planta (Berl) 92 73-84... 

Fig. 3.2. The development of the wheat endosperm. P pericarp, E endosperm, ml meriste-matic layer, twc thick-walled cells, al aleurone layer. The constrictions indicated on the Day 14 sample are now recognised as artefacts of fixation. By Day 16 enough storage material is present to resist distortion. After Evers, 1970 [57]...

It would obviously be of great interest to know whether two distinct patterns of reserve mobilization really do occur within cereals. It is still possible that there is fundamentally only one (GA-dependent) and that the endosperms of maize and sorghum contain sufficient endogenous GA (produced there during development) to stimulate maximum hydrolase production without a requirement for a further supply from the embryo, or without any additional effect of exogenously added GA. The effect of added GA on maize endosperm (aleurone layer) probably varies in different hybrid or inbred lines because some already have a high endogenous GA level while others, e.g. dwarf maize, are naturally deficient in GA. The latter show a three- to five-fold increase in hydrolase production in response to added GA [64] (see Chap. 7). 

A system for the mobilization of stored reserves in the starchy endosperm for use by the developing seedling. This might be comprised of two components proteinase synthesized and secreted by the aleurone layer (and again controlled by GA), and proteinase pre-formed in the endosperm itself and activated therein. 

The catabolites of phytase activity in wheat are myo-inositol, phosphate, and the macroelements potassium, magnesium and calcium. Myo-inositol phosphate ester intermediates with fewer than six phosphate groups do not accumulate within the grain during hydrolysis of the phytin molecule [94], which is indicative of its rapid and complete breakdown by phytases. Movement of the catabolites from the aleurone layer and their redistribution into the developing seedling appears to be by simple diffusion through the endosperm, without any apparent competition for uptake by the scutellum. 

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. 

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