| Phospholipase D (PLD; EC 3.1.4.4) plays an important role in membrane degradation and in mediation of plant responses to stresses. The antisense suppression of two isoforms of PLD, namely PLDalpha and PLDgamma, was accomplished to examine the role of PLD in freezing tolerance and in the growth and development of Arabidopsis thaliana (ecotype- Columia). A significant increase in freezing tolerance was observed under both unhardened and cold acclimated conditions by PLD suppression. For example, the cold-acclimated anti-PLDalpha and anti-PLDgamma plants survived -10.5°C and -13.5°C respectively in contrast to the wild-type plants which survived -7.5°C. Cold responsive genes such as Cor 24, Cor 47, Cor 78, and Rab 18 were induced in PLD-suppressed plants in response to freezing, while they were not activated in wild-type plants. In addition, osmolytes such as proline, raffinose, sucrose, glucose, and glycine betaine accumulated in PLD-suppressed plants at higher levels. Cold acclimation in Arabidopsis plants was associated with water stress, which alone in the absence of cold can induce freezing tolerance.;Suppression of PLD drastically changed the growth and development of the Arabidopsis plants. Anti-PLD plants were taller, had larger canopies, bigger leaves, longer roots, and more cuticular wax than that of the wild-type plants. Moreover, morphology of the trichomes and distribution of the stomata were markedly different from the wild-type plants. Suppression of the PLDgamma gene led to changes in reproductive characteristics, such as delayed flowering time, increased cauline leaves, and altered floral organs (longer pistil and shorter stamens, immature or collapsed pollen), and flower distributions. Other changes included longer siliques and larger seeds. The specific changes in floral development are likely to result in reduced fertility in these plants.;Some of the mutants resulting from transgenic plants were also characterized. The mutant CT-1 derived from wild-type plants was more freeze tolerant. The anti-PLDgamma plants were generally low in fertility and subsequent generations produced a number of phenotypes, which are characterized in this study. |
