PARENT SESSION
Poster Session 35: Evolutionary Ecology
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Self / nonself discrimination in plant shoots.

Raz, Asaf^*,1, Novoplansky, Ariel¹, ¹ Mitrani Department of Desert Ecology, Midreshet Ben-Gurion, Israel

ABSTRACT- Competition usually entails the allocation of limited resources to non-reproductive organs. Natural selection is expected to favor mechanisms that minimize wasteful competition among parts of the same individual. We investigated the possibility that plant shoots are able to discriminate between self and nonself competition for light. The central premise is that shade signals cannot be specific, thus such self/nonself discrimination must rely on probabilities rather than specific information regarding self and nonself shade. We hypothesized that plants attain these probabilities from the relative position of the shaded organ and the direction of the shade they perceive. In Ocimum basilicum, shading of the uppermost part of the seminal stem, simulating competition with nonself neighbors, caused an enhanced stem elongation, whereas shading of the lateral branches at the bottom of the canopy, simulating self shading did not trigger any shade avoidance responses. However, following the removal of the upper parts of the seminal shoot above them, such lateral branches became highly responsive to shade. These results suggest that Ocimum basilicum plants are able to minimize responses to self shading and enhance responses to nonself shading according to the relative position of the shaded branch within the canopy. Seminal shoots of prostrate Portulaca oleracea plants deviated from their original growth direction and enhanced lateral branch development in response to frontal shade that simulated competition with nonself neighbors. Such responses were not observed when similar shade was directed from behind, which simulated an increased level of self shading. Thus, Portulaca oleracea is able to probabilistically differentiate between self and nonself shading according to the direction of the perceived shade. It is suggested that the results are mechanistically based on physiological coordination between organs that belong to the same plant.

Key words: competition, physiological coordination, shoots, self-shading