|Budget Amount *help
¥3,000,000 (Direct Cost : ¥3,000,000)
Fiscal Year 1999 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1998 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1997 : ¥1,300,000 (Direct Cost : ¥1,300,000)
The growth rate of the stem cells is mainly determined by two parameters, the osmotic potential and the mechanical properties of cell walls. Much evidence indicates that white light inhibits shoot elongation in etiolated seedlings by decreasing the mechanical extensibility of cell walls. On the other hand, there is a report suggesting that white light increases osmotic potential, resulting in inhibited stem elongation in etiolated maize seedlings (Parvez et al. 1996). In this report, the mechanism by which white light regulates osmotic properties was studied, in relation to stem growth in maize seedlings.
White light strongly inhibited growth of the coleoptils, while it stimulated growth of the first leaf. Osmotic potential in the coleoptile was increased, in response to the irradiation of white light. On the other hand, white light decreased osmotic potential in the first leaf. Changes in the growth rate in the coleoptile and the first leaf were correlated with changes in osmotic poten
tial. The total amount of osmotica in the coleoptile and first leaf was correlated with that a soluble sugars. White light inhibited the activity of acid invertase bound to cell walls, while it promoted the enzyme activity in the first leaf. The activity of the acid invertase was correlated with the content of soluble sugars in the coleoptile and the first leaf.
In addition to the coleoptile and first leaf, white light also increased osmotic potential in the mesocotyl. In response to the irradiation of white light, the activity of acid invertase decreased in the mesocotyl. Sugar exudation from the cut of the segments excised from the coleoptile and the mesocotyl in the presence of EDTA was stimulated by white light irradiation. The mesocotyl was cut 10 mm above the caryopsis, to examine the effect of light on sugar transport from the caryopsis to the mesocotyl. Sugar exudation from the cut of the mesocotyl was not influenced by light irradiation. Vanadate a potent inhibitor of plasma membrane-proton ATPase nullified the effect of white light on sugar exudation from the cut of the coleoptile and the mesocotyl.
From these experimental results, it was concluded that white light controls shoot growth in maize seedling by controlling sugar distribution among organs in maize seedlings via controlling the activity of acid invertase bound to cell walls. At present, the cloning of acid invertase gene is in progress, to study the regulatory mechanism of the gene expression on acid invertase in organs in maize seedlings during photomorphogenesis. Less