Regulation of Leaf Shape in Proserpinaca palustris

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Abstract
Submerged shoots of Proserplnaca palustrls have finely dissected leaves whether grown in long or short photo-periods, while leaves of aerial shoots are dissected in short days but expanded-lanceolate in long days. Shoot habit, internode length, and leaf orientation are also varied in these different environments. High light intensity or elevated temperature may induce aerial leaf shape and shoot morphology long-day submerged shoots. When a shoot is transferred abruptly to a new environment a series of transitional leaf forms is produced. The number of transitional leaves depends on the number of immature leaves in the bud, which in turn depends on the environment in which the shoot had been growing. Leaf primordia in contrasting environments are identical in form until 500-600 [mu]. When the primordia are 500-600 [mu] long, 5 lobe pairs have been initiated in basipetal succession by accelerated cell division at sites along the marginal meristems. At this stage morphological differences become apparent; these Involve differential distribution of cell division in lobes and sinus regions. Cell surface replicas revealed only limited differences in cell shape in dissected and expanded aerial leaves. However, in plnnatlfid submerged leaves, polar elongation of cells of the lobes and midrib Is associated with the larger, more finely dissected leaf form. Further, long-day leaves develop more lobes than short-day leaves, and the rate of leaf development per plastochron is faster in long-day shoots. Heterophylly of amphibious plants is discussed, including possible mechanisms by which the environmental stimulus may regulate the elemental processes of cell division and polar cell expansion which are involved in shaping the leaf.