Phototropic Leaflet Reorientation in Alfalfa Germplasm Selected for Leaf Color and Size

Abstract

AbstractSolar tracking has been described in several agronomic and wild species, yet variation within a given species has not been reported. To address that issue, photoperiod leaflet reorientation in response to vectorial light was measured in three alfalfa (Medicago sativa L.) germplasm pools selected from the cultivar Ladak 65. Dark‐leaf germplasm responded to all photosynthetic photon flux densities (PPFD) (100 to 700 μmol/m2/s) with no detectable lag period. Following a 24‐h dark treatment only high PPFD (600 to 700μmol/m2/s) elicited reorientation. Pale‐leaf germplasm responded to intermediate (300 to 400 μmol/m2/s) and high PPFD in a similar manner; however, the low (100‐125μmol/m2/s) PPFD treatment had little effect on reorientation. The 24‐h dark treatment decreased reorientation at all PPFD. Small‐leaf germplasm responded equally to all PPFD and was not affected by the 24‐h dark treatment. The results suggest that available energy levels may influence the reorientation response. Carbonyl cyanide m‐chlorophenylhydrazone, an inhibitor of photophosphorylation, and 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea, an inhibitor of non‐cyclic photosynthetic electron transport, reduced reorientation only in the pale‐leaf type. These results suggest that stored energy reserves were adequate to maintain leaflet reorientation in the absence of photosynthesis in all but the pale‐leaf germplasm. In that germplasm photosynthetically generated energy may be required to support reorientation.