IMPACT OF DIFFERENTIATED INSTRUCTION ON ACHIEVEMENT IN TEACHING MATHEMATICS TO LOWER-STAGE GRADES

Abstract

Two low-molecular-weight proteins have been purified from Brassica napus pollen and a gene corresponding to one of them has been isolated. The gene encodes an 8.6-kD protein with two EF-hand calcium-binding motifs and is a member of a small gene family in B. napus. The protein is part of a family of pollen allergens recently identified in several evolutionarily distant dicot and mono-cot plants. Homologs have been detected in Arabidopsis, from which one gene has been cloned in this study, and in snapdragon (Antirrhinum majus), but not in tobacco (Nicotiana tabacum). Ex-pression of the gene in B. napus was limited to male tissues and occurred during the pollen-maturation phase of anther develop-ment. Both the B. napus and Arabidopsis proteins interact with calcium, and the potential for a calcium-dependent conformational change was demonstrated. Given this affinity for calcium, the cloned genes were termed BPC1 and APC1 (B. napus and Arabidop-sis pollen calcium-binding protein 1, respectively). Immunolocal-ization studies demonstrated that BPC1 is found in the cytosol of mature pollen. However, upon pollen hydration and germination, there is some apparent leakage of the protein to the pollen wall. BPC1 is also concentrated on or near the surface of the elongating pollen tube. The essential nature of calcium in pollen physiology, combined with the properties of BPC1 and its high evolutionary conservation suggests that this protein plays an important role in pollination by functioning as a calcium-sensitive signal molecule. Pollination is a complex process involving an intricate series of physiological changes in the pollen and interac-tions between the pollen grain and stigma, which culmi-nates in the successful fertilization of the egg (for review, see Dumas et al., 1994; Elleman and Dickinson, 1994). The pollen grain lands on the stigma in a desiccated, metabol-ically inactive state. In Brassica, a conduit is formed be-tween the pollen grain and a stigmatic papillary cell to