The Dorsiventrality of Leaf Primordia

Abstract

summary When in shoot apices of potatoes the presumptive area of I1, the next leaf due to arise, or of 12, was isolated from the growing‐point by a vertical cut, the isolated pieces regularly formed dorsiventral leaves, even when slips of mica were left in the cuts. These results differ from those of Sussex, who reported that he obtained radial leaves from nearly similar operations on potatoes, and interpreted them as due to interruption of an induction of dorsiventrality by the apex. The difference in the results cannot be explained by supposing that our isolated pieces were larger than his, since the evidence indicates that they were smaller. It may have been due to differences in the conditions of culture. In apices of Epilobium hirsutum on the other hand, I1 areas when isolated by vertical cuts developed often into radial leaves, though sometimes into dorsiventral leaves. So also did P, primordia if isolated on small pieces at early plastochron. These and other experiments on E. hirsutum make it probable that in that species the dorsiventrality of the leaves is induced by the apex. But this cannot be concluded with certainty, since the experiments show also that reduction of size contributes towards making an isolated I1 or P1 develop as a radial leaf, and it remains possible that this factor may have been effective alone. In earlier experiments on E. hirsutum P1, I, or I2 was narrowly confined between two vertical radial cuts, without being isolated from the apex, and several of these confined primordia or presumptive areas formed radial leaves, which are illustrated. But in more numerous later experiments this result was not obtained again. The determination of the dorsiventrality of leaves in these and other species is briefly discussed.

Regulation ofArabidopsisshoot apical meristem and lateral organ formation by microRNAmiR166gand itsAtHD-ZIPtarget genes

“…Given that PHB and PHV confer adaxial identity (Emery et al, 2003;McConnell and Barton, 1998), the adaxialization of jba-1D leaves seems counterintuitive. However, experiments have shown that a SAM-derived signal(s) is important for specifying adaxial leaf identity (Snow and Snow, 1959;Sussex, 1954;Waites and Hudson, 1995), and thus initiating jba-1D leaves may receive an excess of adaxializing signal(s) emanating from multiple SAMs. Increased accumulation of transcripts from REV, which plays a redundant role with PHB and PHV in conferring adaxial fate (Emery et al, 2003), may also contribute to conditioning this phenotype, as increased meristem size per se is not sufficient to cause leaf adaxialization (Clark et al, 1993).…”

The Arabidopsis LATERAL ORGAN BOUNDARIES-Domain Gene ASYMMETRIC LEAVES2 Functions in the Repression of KNOX Gene Expression and in Adaxial-Abaxial Patterning

“…These asymmetries are established relatively early during leaf development and are defined relative to the SAM. Surgical experiments designed to examine the relationship between leaf development and the SAM demonstrated that communication between the SAM and leaf primordia is necessary for the establishment of the adaxial-abaxial pattern and for leaf outgrowth (Sussex, 1955;Snow and Snow, 1959). These experiments suggested the existence of a SAM-derived signal that is necessary for the establishment of adaxial-abaxial leaf polarity.…”

Compound leaves: equal to the sum of their parts?

“…Additionally, signals that emanate from the meristem act to promote development of the adaxial domain of leaves. Incisions that isolate the incipient leaf primordium from the meristem result in radialized leaves that lack an adaxial domain (Sussex, 1954;Sussex, 1955;Snow and Snow, 1959). This suggests that in the absence of the signal(s) from the meristem, the default state is development of the abaxial domain.…”