Analysis of the control of development in Oryzopsis miliacea by the light environment

The developmental responses of Oryzopsis miliacea plants to the light environment were separated into those resulting from the level of incident solar radiation and those resulting from the photoperiod (comparing 16 h, which are inductive for flowering, with 8 h, which are not). The rate of leaf appearance and the transition from the vegetative to the reporductive state, were determined by photoperiod and not by radiation level. In inductive photoperiods, the ontogenetic timing of internode elongation was unaffected by radiation level. Lowering the radiation level progressively delayed and reduced the activation of axillary buds and crown roots, whereas photoperiod was without significant effect. Accumulation of dry matter was progressively reduced as the radiation level was lowered, without affecting its distribution between the root and shoot systems. The mean dry-matter content of a single shoot, as well as that of a single crown root, were also unaffected by radiation level. The shorter photoperiod resulted in the diversion of a greater proportion of the dry matter to the root system, with the result that individual shoots accumulated less, and individual roots accumulated more dry matter than in the longer photoperiod. Leaf blades in comparable nodal positions were consistently smaller and contained less vasucular bundles in the longer photoperiod. These effects were apparently due to inhibition of the trend for increasing cell proliferation in the surface plane by the long photoperiod, and its very small effect on the trend for diminution in cell dimensions in blades on progressively higher nodes. The level of solar radiation also affected blade surface dimensions, lower levels resulting in progressively larger surfaces, but the effects of photoperiod and those of nodal position were equally modified. The longer photoperiod reduced the cross-sectional area of the interbundle chlorenchyma strands, without affecting its shape, while reduction in radiation level caused an increase in its width and a compensating decrease in its thickness, thus changing the shape of the cross-section without affecting its area.