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Pollen selection under acid rain stress
Abstract
To investigate whether acid rain stress induces pollen selection in nature, three different approaches were used, based on the assumption that the response of pollen grains to acid rain is controlled by an acid sensitive gene product. The first approach was to examine the germination of pollen from homozygous and heterozygous individuals under acid rain stress to detect any differences in the rate of germination between populations of homogeneous and heterogeneous pollen grains. The second and third approaches were in vitro and in vivo bulked segregant analysis using RAPDs to search for differences in DNA constitution between the survivors of acid rain stressed and non-acid rain stressed pollen populations in vitro and between the progenies of acid rain stressed and non-acid rain stressed populations during pollination, respectively. No evidence for the pollen selection under acid rain stress was obtained in any of our test systems. To determine whether protein synthesis was involved in the response of pollen grains to acid rain stress, a protein synthesis inhibitor, cyclohexmide, and 2-dimensional electrophoresis were used. During first 2 hours of incubation corn pollen tube growth was not retarded by inhibition of protein synthesis using cyclohexmide. In contrast, simulated acid rain at pH 4.5 demonstrated significant inhibitive effect on tube elongation at 0.5 hr. Inhibition of protein synthesis using cycloheximide led to significant reduction of tube elongation at 4 hr and had no effect on pollen germination at any time interval tested. Total proteins extracted from control and acid rain stressed pollen grain populations cultured for 2 hr exhibited no differences as revealed by 2-dimensional gel electrophoresis. The reduction of corn pollen germination in vitro under acid rain stress was mainly due to pollen rupture. In one test, at pH 5.5, germination was 55% and a few grains ruptured; at pH 4.5, germination was 13% and rupture was 70% of the pollen; at pH 3.5, no germination nor rupture occurred. Pollen rupture on a pH 4.5 medium was prevented when the respiratory inhibitor, KCN, was incorporated in the medium or when the pollen grains were kept at 4$\sp\circ$C. The present data indicates the reduction of pollen germination and tube growth under acid rain stress may be a physiological response rather than a genetic response. A simple, nontoxic, and effective method to separate germinated from ungerminated pollen grains has been developed using pollen from corn (Zea mays, L. cv. Pioneer 3747). After separation, 99.1% of the grains in the sample of germinated pollen grains had tubes; 97.2% of the grains in the sample of ungerminated pollen grains had no tubes. Recovery was 18.1% of the total grains for germinated and 1.5% for ungerminated pollen grains. The separated germinated pollen grains retained viability and continued tube growth when placed in culture medium.
Subject Area
Genetics|Plant sciences
Recommended Citation
Zhang, Yuanhai, "Pollen selection under acid rain stress" (1994). Doctoral Dissertations Available from Proquest. AAI9420700.
https://scholarworks.umass.edu/dissertations/AAI9420700