Proline Content of the Anthers and Pollen of Heat‐Tolerant and Heat‐Sensitive Cowpea Subjected to Different Temperatures

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Abstract
High temperatures cause reductions in grain yield of cowpea [(Vigna unguiculata (L.) Walp.] that are associated with low pollen viability and pod set. Preliminary controlled environment studies showed differences in proline accumulation in anthers and pollen of heat‐tolerant and heat‐sensitive genotypes under hot and optimal temperatures, but insufficient tissue was available to establish if the differences were significant. The objective was to determine whether heat injury under field conditions is associated with specific patterns of proline accumulation in leaves and reproductive tissue using heat‐sensitive an heat‐tolerant cowpea genotypes. Under moderate and hot temperatures, proline was the most abundant free amino acid in the anthers of both heat‐sensitive and heat‐tolerant cowpea genotypes. No differences in leaf proline concentrations were observed. Under hot conditions, proline levels in anthers decreased faster as pollen matured in heat‐tolerant genotypes as compared with heat‐sensitive genotypes. At pollen maturity, heat‐sensitive genotypes contained more proline in anthers and had lower levels in pollen than the heat‐tolerant genotypes under hot conditions but similar levels under more optimal temperatures. The results suggest that heat injury during floral development of sensitive cowpea genotypes may be due to inhibition of proline translocation from anther walls to pollen.