Plant physiology

About: Plant physiology is a research topic. Over the lifetime, 1537 publications have been published within this topic receiving 72038 citations.

Can stress-induced CAM provide for performing the developmental program in Mesembryanthemum crystallinum plants under long-term salinity?

Abstract: The development of CAM-type photosynthesis is one of the adaptation mechanisms to severe water deficit. It provides plants with carbon dioxide and permits efficient water spending under extreme environments. In common ice plants, a complete switch from C3 to CAM photosynthesis was observed on the seventh day of salinity (0.5 M NaCl). The indices characterizing this switch were: (1) induction of phosphoenolpyruvate carboxylase; (2) diurnal changes in the organic acid content, which are characteristic of CAM plants, and (3) suppression of transpiration during the daytime. A decrease in the osmotic potential (ψπ) of the leaf sap, which occurred on the second day of salinity, preceded these changes. After long-term salinity stress (four–five weeks), ψπ attained extremely low values (–4.67 MPa), which made possible the water uptake by the root system. The restoration of the ψπ balance between cell compartments resulted from the accumulation of compatible solutes in the cytoplasm, proline primarily, which possesses osmoregulatory and stress-protective properties. This means that a complex of adaptive mechanisms is required for the realization of the common ice developmental program under salinity. These mechanisms maintained plant capacity to uptake water and permitted its efficient utilization. They triggered the development of stress-induced CAM-type photosynthesis, maintained the low osmotic potential in the cell sap, regulated the composition of macromolecules in the cell microenvironment, provided for water storage in tissues, and reduced the time of plant development. A comparison between the time-courses of CAM development and a decrease in the transpiration rate permitted us to suggest that a combination of low ψπ and CO2 in the leaf cells could serve as a signal for the induction of CAM-dependent gene expression in terrestrial plants.

Dynamics of growth and the content of endogenous phytohormones during kidney bean scoto-and photomorphogenesis

Abstract: The dynamics of growth and the contents of free and bound endogenous IAA, gibberellins (GA), cytokinins (zeatin and its riboside), and ABA in kidney bean plants (Phaseolus vulgaris L., cv. Belozernaya) grown in darkness or in the light was studied. Phytohormones were quantified in 5–15-day-old plants by the ELISA technique. Plant growth and phytohormone content were shown to depend on plant age and the conditions of illumination. During scotomorphogenesis, changes in the biomass and hypocotyl length were highly correlated with the content of GA, whereas during photomorphogeneses, these parameters were correlated with the content of zeatin. In darkness, epicotyl growth displayed a positive correlation with the content of GA, whereas in the light, the correlation was negative. Growth characteristics of the primary leaves were shown to correlate with IAA in darkness and with GA and zeatin in the light. At a low concentration of cytokinins in illuminated leaves, cell divisions occurred, whereas, at the higher cytokinin concentrations, cell expansion occurred. The highest content of GA was characteristic of leaves in the period of growth cessation. ABA accumulated during active leaf and root elongation and biomass increment in the light and during hypocotyl growth in darkness. After plant illumination, the ratio of auxins to cytokinins increased in bean roots and decreased in their epicotyls. Thus, light changed the developmental programs of bean plants, which was manifested in the changed rate and duration of growth of various organs (root, hypocotyl, epicotyl, and leaf). Some mechanisms of light action depended on the contents of IAA, ABA, GA, and cytokinins and the ratios between these phytohormones. Differences between scotonorphogenesis of mono-and dicotyledonous plants are discussed in relation to the levels of phytohormones in them.

Photosynthesis, photosystem II efficiency, amino acid metabolism and ion distribution in rice (Oryza sativa L.) in response to alkaline stress

Abstract: Alkalies are important agricultural contaminants complexly affecting plant metabolism. In this study, rice seedlings were subjected to alkaline stress (NaHCO3:Na2CO3 = 9:1; pH 8.9) for 30 days. The results showed that stress mightily reduced net photosynthetic rate (PN), but slightly decreased transpiration rate and stomatal conductance. This indicated that decline of PN might be a result of nonstomatal factors. Alkaline stress caused a large accumulation of Na+ in leaves up to toxic concentration, which possibly affected chloroplast ultrastructure and photosynthesis. We found that alkaline stress reduced chlorophyll fluorescence parameters, such as ratios of Fv′/Fm′, Fv/Fm, photosystem (PS) II efficiency, and electron transport rates in rice plants, i.e. it influenced the efficiencies of photon capture and electron transport by PSII. This might be a main reason for the decrease of PN under such conditions. Deficiency of minerals could be another reason for the decline of PN. Alkaline stress lowered contents of N, K, Cu, Zn, P, and Fe in rice plants. In addition, the stress strongly affected metabolism of amino acids. This might be caused by imbalance in carbon metabolism as a result of photosynthesis reduction.

Gibberellin involvement in dormancy-break and germination of seeds of celery (Apium graveolens L.)

Abstract: The temperature-dependent, primary dormancy of cv. Florida 683 celery seeds in darkness was partially broken by a 30 min light exposure on the third day of incubation at 20–22°C, resulting in c 50 percent germination after 20 days. This light stimulation was negated by including different inhibitors of gibberellin biosynthesis in the incubation medium. Subsequent addition of a solution of the gibberellins A4 and A7 or of the gibberellin-active compound (1-3-chlorophthalimido)-cyclohexane carboxamide (AC94,377) overcame the inhibitory effects on germination of these GA-biosynthesis inhibitors. It is suggested that light stimulates the biosynthesis of gibberellins which are essential for dormancy-break in celery seeds and that this biosynthesis is either directly or indirectly controlled through phytochrome.

Relationships between nitrogen fixation and photosynthesis as the main components of the productivity in alfalfa

Abstract: Alfalfa (Medicago sativa L.) plants were inoculated with Sinorhizobium meliloti Tn-5 mutants featuring various nitrogen-fixing effectiveness and then grown in sand culture to study relations between CO2 exchange, plant productivity, and nitrogen fixation. At the flowering stage, the relationship between nitrogen fixation and photosynthesis of whole alfalfa plants was described with the logarithmic curve. At the same stage of plant development, a close relationship was observed between nitrogen fixation rate and plant weight; this relationship showed a trend toward saturation at high rates of nitrogen fixation. The increase in nitrogenase activity of root nodules was accompanied by stimulation of root respiration; the relation of respiration to nitrogen-fixing activity was manifested stronger than its relation to the total root weight. It is concluded that highly effective strains of root nodule bacteria can realize their potential only in combination with complementary plant genotypes featuring active photosynthesis that provides a balanced supply of assimilates for both the symbiotic apparatus and growth processes in the macrosymbiont.