Expression of cell cycle regulatory genes and morphological alterations inresponse to salt stress in Arabidopsis thaliana

Hyperosmotic stress severely affects plant growth and development. To exami ne the effect of salt stress on cell cycle activity in Arabidopsis thaliana (L.) Heynh., the transcriptional regulation of a cyclin-dependent kinase, CDC2aAt, and two mitotic cyclins, Arath;CycB1;1 and Arath;CycA2;1, was stud ied by using the P-glucuronidase (gus) reporter gene. Moreover, the mRNA ab undance of these cell cycle genes as well as CDC2bAt were monitored during salt stress, Upon NaCl treatment, the promoter activities and transcript le vels of all cell cycle genes diminished initially in the shoot apex and wer e subsequently induced during salt-stress adaptation. Additionally, the pro moter activities of CDC2aAt and CycA2;1 decreased in the vascular cylinder of the root in correlation with reduced lateral root formation. In the root tips, a regression of CDC2aAt, CycA2;1, and CycB1;1:gus expression was obs erved, concomitant with a shrinkage of the root meristem and inhibition of root growth. Our data indicate that salt stress interferes with cell cycle regulation at the transcriptional level, resulting in an adaptive growth re sponse.