Activity Of Tonoplast Research Articles

A Prominent Role for Leaf Calcium as a Yield and Quality Determinant in Upland Cotton (Gossypium hirsutum L.) Varieties Grown Under Irrigated Mediterranean Conditions

Seven cotton (Gossypium hirsutum L.) accessions were tested over 2 years under irrigated Mediterranean conditions on a loamy soil with nitrogen (N) as the only nutrient input. The study aimed to identify the critical nutritional and physiological factors determining seedcotton yield and fibre quality. A suite of leaf physiological traits [chlorophyll content (assessed by SPAD), carbon isotope discrimination (Δ), 15N natural abundance (δ15N), leaf water potential, N and C concentrations, C/N ratio, K, Na, Ca and Mg concentrations, their sum and ratios] was assessed, and their interrelationships then analysed. It was found that physiological indices such as SPAD, Δ and δ15N failed to discern genotypes for yield and did not relate with fibre quality traits. At the same time, leaf Ca concentration was the trait that showed the strongest correlation with both seedcotton (SY) and lint yield (LY). An increase of K/Na ratio up to 5.74 was beneficial for SY but higher ratios impacted yield adversely. In this line, exclusion of K in favour of Ca (lower K/Ca ratios) increased both SY and LY. The above results could be explained by Ca2+ control over activity of tonoplast and plasma membrane cation channels, resulting in redistribution of K+ between cell compartments. It is suggested that Ca2+-rich plants are more efficient in sequestering higher K+ quantities in leaf vacuoles, at the expense of cytosolic K+. Under K+-limiting conditions, such redistribution may trigger programmed cell death and enhance leaf senescence. This would remobilize and translocate nutrients (e.g. N) and organic substances to sinks (seedcotton), contributing to higher yields reported in the present work.

Interaction of signal systems (nitric oxide and calcium) in regulation of hydrolytic activity of tonoplast H+-pyrophosphatase under normal conditions and stress

The dependence of the functioning of the main components of membrane transport systems on the effect of signal molecules regulating homeostasis in the plant cells has not been practically studied so far. According to modern notion, the key signal molecules are nitric oxide and calcium ions. Nitric oxide is a ver� satile endogenous compounds regulating metabolism in organisms at different stages of evolutionary devel� opment. The role of NO as a key signal molecule in plants has been established fairly recently [1] and is now intensively studied. It was shown that, in animal cells, NO regulates Ca 2+ homeostasis [2]. In plants,

Study on the salt and drought tolerance of Suaeda salsa and Kalanchoe claigremontiana under iso-osmotic salt and water stress

Seedlings of Suaeda salsa and Kalanchoe claigremontiana grown in plastic pots were treated with (1) Hoagland's nutrient solution, (2) 100 mM NaCl, (3) 50 mM NaCl+PEG ( M W 6000) iso-osmotic to 50 mM NaCl, (4) PEG iso-osmotic to 100 mM NaCl. After 2 weeks, the plant fresh and dry weight, organic and inorganic osmotica, osmotic adjustment ability, subcelluar distribution of Na + and Cl −, and the activities of tonoplast H +–ATPase and H +–PPase were determined. Results found that euhalophyte S. salsa grew best with 100 mM NaCl, but worst with iso-osmotic PEG and died after 6 days. However, the growth of K. claigremontiana was not significantly inhibited by PEG iso-osmotic to 100 mM NaCl, but dramatically inhibited by 100 mM NaCl and died after 8 days. The subcellular analysis of Na + and Cl − in fully mature leaves revealed that S. salsa retained Na + and Cl − in the vacuoles, while Na + and Cl − of K. claigremontiana was mainly distributed in the cytoplasm. The analysis of tonoplast H +–ATPase activity and H +–PPase hydrolysis activity demonstrated that the enzyme activities were much more prompted by NaCl in S. salsa than in K. claigremontiana, which was closely related to the salt inclusion capacity in S. salsa. The results pointed out that S. salsa was salt-tolerant and drought-tolerant, only when the low water potential of the latter was caused by high Na + and Cl − concentration.

Nitrate transport across the tonoplast of Cucumis sativus L. root cells

Nitrate transport across the tonoplast has been studied using vacuole membranes isolated from cucumber roots grown in nitrate. The addition of NO3- ions into the tonoplast with ATP-generated transmembrane proton gradient caused the dissipation of delta pH, indicating the NO3(-)-induced proton efflux from vesicles. NO3(-)-dependent H+ efflux was almost insensitive to the transmembrane electrical potential difference, suggesting the presence of an electroneutral NO3-/H+ antiporter in the tonoplast. Apart from saturation kinetics, with respect to nitrate ions, NO3(-)-linked H+ efflux from the tonoplast of cucumber roots showed other characteristics expected of substrate-specific transporters. Experiments employing protein modifying reagents (NEM, pCMBS, PGO and SITS) indicated that a crucial role in the activity of tonoplast nitrate/proton antiporter is played by lysine residues (strong inhibition of NO3-/H+ antiport by SITS). None of the ion-channel inhibitors (NIF, ZnSO4 and TEA-Cl) used in the experiments had a direct effect on the nitrate transport into tonoplast membranes. On the other hand, every protein reagent, as well as NIF and ZnSO4, significantly affected the ATP-dependent proton transport in vesicles. Only TEA-Cl, the potassium channel blocker, had no effect on the vacuolar proton pumping activity.

Effects of Gamma-Irradiation on the Activity of Tonoplast H+-ATPase from Potato Tubers (Solanum tuberosum L.)

Effects of Gamma-Irradiation on the Activity of Tonoplast H+-ATPase from Potato Tubers (Solanum tuberosum L.)

Tonoplast and plasma membrane ATPases from maize lines of high or low vigour

AbstractThe effectiveness of ATPase in germinated seed may play an important role in the vigour of germination. The activities of tonoplast and plasma membrane ATPases in two maize (Zea maysL.) lines with different vigour of germination were determined. ATP hydrolysis was measured in microsomal fractions from coleoptiles along with the responses to specific inhibitors for the plasma membrane, tonoplast and mitochondrial ATPases as well as for acid phosphatase. Nitrate-sensitive ATPase activity was 1.5–3.0 times lower in the low-vigour line than in the high-vigour line. Kinetic analysis of ATP hydrolysis at different substrate concentrations revealed the existence of two enzymes in the microsomal fractions of the two lines. TheVmaxof enzyme 1 in the low-vigour line was a third of that in the high-vigour line. This enzyme was identified as the nitrate-sensitive or tonoplast ATPase on the basis of measurements of ATP hydrolysis in the presence of specific inhibitors at high (8.12mm) and low (0.77mm) ATP concentrations.

Impairment of Tonoplast H+-ATPase as an Initial Physiological Response of Cells to Chilling in Mung Bean (Vigna radiata [L.] Wilczek)

Biochemical alterations of cellular membranes in chilling-sensitive mung bean (Vigna radiata [L.] Wilczek) hypocotyls were investigated with reference to chilling injury. Reversible decreases in activities of tonoplast H(+)-ATPase and in vivo respiration became manifest within 24 hours of chilling when tissues suffered no permanent injury as assessed by electrolyte leakage and regrowth capacity. These changes were found to be the earliest cellular responses to chilling. A density-shift on a sucrose density gradient was observed in Golgi membranes early in the chilling treatment, suggesting that Golgi function and/or membrane biogenesis via the Golgi may have been altered upon chilling. After chilling more than 2 days, irreversible changes were generally produced in cellular membranes including the plasma membrane, endoplasmic reticulum, and mitochondria. Respiratory functions remained intact in mitochondria isolated from tissues prechilled for 24 hours, but were impaired after prechilling for 3 days. Given the important role of the tonoplast H(+)-ATPase in the active transport of ions and metabolites, the early decline in the tonoplast H(+)-ATPase activity may give rise to an alteration of the cytoplasmic environment and, consequently, trigger a series of degenerative reactions in the cells.