The physiology of growth in Subterranean clover. II. The dynamics of leaf growth

Abstract

This study extends the account of the development of the fourth leaf of subterranean clover. In particular, the four leaf constituents deoxyribonucleic acid, ribonucleic acid, proteins, and cell wall materials are expressed on whole leaf and cell bases.

Form change in the leaf is illustrated with perspective elevations for some early stages.

Cell number increases exponentially until day 13, with a mean generation time of 18 hr. The final number per leaf is c. 6.5 million, and deoxyribonucleic acid phosphorus is estimated as 0.197 pg per cell.

The leaf is highly succulent, with a maximum water content of 478 % dry weight. Soluble constituents are also high, with a maximum of 39 % of the dry matter.

The absolute amounts of ribonucleic acid phosphorus and protein nitrogen are maximal on days 19 and 25 respectively, with losses of about 60% by day 36.

Cell wall materials increase from 8 to 57 % of the residual dry weight during a period of 4 days prior to emergence. This is shown to be due to the concurrent differentiation of the vascular system and the growth of 3000 leaf hairs.

Changes on a per cell basis are recorded, and the concept of relative growth rate is used to extend the analysis of the data. Rates of production of one constituent per unit of another are also presented and discussed.