Synthesis of DNA in excised watermelon cotyledons grown in water and benzyladenine

Isolation of a cDNA clone for a cytokinin-repressed gene in excised cucumber cotyledons

Rapid changes in gene expression were studied during incubation of cucumber (Cucumis sativus L.) cotyledons with cytokinins in darkness. Complementary-DNA clones for mRNAs whose levels decreased within 4 h of treatment with N6-benzyladenine (BA) were isolated by differential hybridization. One of them (CR9) was sequenced. It is 588 bp long, and would encode a protein consisting of 137 amino-acid residues and having a molecular mass of 15 kDa. The sequence shows a high homology with a light-induced gene from rice. Northern blot analysis of the CR9 transcript showed the level of the mRNA (0.7 kb) to decrease tenfold within 4 h of BA treatment, i.e. well before BA-induced cotyledon expansion was observed. The repression became greater with increasing concentration of BA (10(-8)-10(-5) M). The expression of the CR9 gene was repressed specifically by cytokinins (BA, isopentenyladenine and t-zeatin), but not by adenine or 2,4-dichlorophenoxyacetic acid (auxin). The results are discussed in relation to the primary action of cytokinin.

Changes in translatable poly(A) RNA from differentiated potato tissues transformed with shoot-inducing Ti TL-DNA of Agrobacterium tumefaciens

Two dimensional gel electrophoresis was used to examine differences in steady state total poly(A) RNA from untransformed potato (Solanum tuberosum cv. Maris Bard) and potato transformed with shoot-inducing TL-DNA from A. tumefaciens. RNA was compared from phenotypically very distinct in vitro cultured shoots, more similar grafted plants and tubers. In each case between 200-400 translation products were identified representing the more abundant poly(A) mRNA's. In general, poly(A) RNA from the transformed tissues gave more high molecular weight products. This increase was most evident in poly(A) RNA from shoot cultures. Depending on the tissue examined, 1-5% of the translation products with a molecular weight <43 KD were observed to increase or decrease in abundance. The influence of T-DNA on cellular gene expression in the different transformed potato tissues is discussed in relation to previously determined changes in T-DNA gene expression (particularly of the T-DNA cytokinin gene) and the corresponding changes in endogenous hormone concentrations. It is concluded that some of the specific changes in low molecular weight products are either directly caused by the increased cytokinin levels or are indirectly involved in maintaining the transformed phenotype. re]19850530 rv]19851206 ac]19851210.