Cytokinin-induced decrease in ribonuclease activity and initiation of gametophore buds in the protonema of mosses

As early as after 4 hours of kinetin treatment a decrease in RNase activity was found in the moss protonema and it was maintained to at least 10 hours. It was shown that this decrease was correlated with the morphogenetic effect of kinetin (bud induction). No allosteric inhibition of RNase toy kinetin could be found. The decrease in enzyme activity was more pronounced When additionally inhibitors of protein and RNA synthesis were used. It is concluded that kinetin affects the RNase rather by an inhibition of de novo synthesis of the enzyme than by an increase of its decomposition by proteases.

Effect of 2-chloroethylphosphonic acid and vanillin on chlorophyll, protein and RNA synthesis in detached cucumber cotyledons, and chlorophyll degradation in senescing leaf discs of kale

N⁶-benzylaminopurine (BAP) and KC1 stimulated growth in detached greening cucumber cotyledons; BAP enhanced RNA synthesis whereas KCl strikingly accelerated leucine-¹⁴C incorporation into proteins. Vanillin (0.01 M) inhibited greening and protein synthesis, and nullified the stimulatory effects of KC1. a-chloroethylphosphonic acid (CEPA, 0.01 M) inhibited greening without any effect on protein synthesis when it was applied alone; CEPA decreased RNA synthesis, completely nullified the K⁺-induced synthesis of chlorophyll, and reduced the BAP^- or KCl^-induced growth. Vanillin inhibited yellowing in 'senescing leaf discs of kale kept in darkness, whereas CEPA had an opposite effect.

Physiological Responses to Starvation in the Marine Oligotrophic Ultramicrobacterium Sphingomonas sp. Strain RB2256

ABSTRACT Sphingomonas sp. strain RB2256 is representative of the ultramicrobacteria that proliferate in oligotrophic marine waters. While this class of bacteria is well adapted for growth with low concentrations of nutrients, their ability to respond to complete nutrient deprivation has not previously been investigated. In this study, we examined two-dimensional protein profiles for logarithmic and stationary-phase cells and found that protein spot intensity was regulated by up to 70-fold. A total of 72 and 177 spots showed increased or decreased intensity, respectively, by at least twofold during starvation. The large number of protein spots (1,500) relative to the small genome size (ca. 1.5 Mb) indicates that gene expression may involve co- and posttranslational modifications of proteins. Rates of protein and RNA synthesis were examined throughout the growth phase and up to 7 days of starvation and revealed that synthesis was highly regulated. Rates of protein synthesis and cellular protein content were compared to ribosome content, demonstrating that ribosome synthesis was not directly linked to protein synthesis and that the function of ribosomes may not be limited to translation. By comparing the genetic capacity and physiological responses to starvation of RB2256 to those of the copiotrophic marine bacteriumVibrio angustum S14 (J. Ostling, L. Holmquist, and S. Kjelleberg, J. Bacteriol. 178:4901–4908, 1996), the characteristics of a distinct starvation response were defined forSphingomonas strain RB2256. The capacity of this ultramicrobacterium to respond to starvation is discussed in terms of the ecological relevance of complete nutrient deprivation in an oligotrophic marine environment. These studies provide the first evidence that marine oligotrophic ultramicrobacteria may be expected to include a starvation response and the capacity for a high degree of gene regulation.