Tobacco (Nicotiana tabacum; C3) plants increase their water use efficiency (WUE) under abiotic stress and are suggested to show characteristics of C4 photosynthesis in stems, petioles, and transmitting tract cells. The tobacco stress-induced Aquaporin1 (NtAQP1) functions as both water and CO 2 channel. In tobacco plants, overexpression of NtAQP1 increases leaf net photosynthesis (A N ), mesophyll CO 2 conductance, and stomatal conductance, whereas its silencing reduces root hydraulic conductivity (L p ). Nevertheless, interaction between NtAQP1 leaf and root activities and its impact on plant WUE and productivity under normal and stress conditions have never been suggested. Thus, the aim of this study was to suggest a role for NtAQP1 in plant WUE, stress resistance, and productivity. Expressing NtAQP1 in tomato (Solanum lycopersicum) plants (TOM-NtAQP1) resulted in higher stomatal conductance, whole-plant transpiration, and A N under all conditions tested. In contrast to controls, where, under salt stress, L p decreased more than 3-fold, TOM-NtAQP1 plants, similar to maize (Zea mays; C4) plants, did not reduce L p dramatically (only by approximately 40%). Reciprocal grafting provided novel evidence for NtAQP1's role in preventing hydraulic failure and maintaining the whole-plant transpiration rate. Our results revealed independent, albeit closely related, NtAQP1 activities in roots and leaves. This dual activity, which increases the plant's water use and A N under optimal and stress conditions, resulted in improved WUE. Consequently, it contributed to the plant's stress resistance in terms of yield production under all tested conditions, as demonstrated in both tomato and Arabidopsis (Arabidopsis thaliana) plants constitutively expressing NtAQP1. The putative involvement of NtAQP1 in tobacco's C4-like photosynthesis characteristics is discussed.

The supply of energy for stomatal opening was investigated with epidermal peels of Commelina communis L. and Vicia faba L., under white, blue and red irradiation or in darkness. Fluencerate response curves of stomatal opening under blue and red light were consistent with the operation of two photosystems, one dependent on photosynthetic active radiation (PAR) and the other on blue light, in the guard cells. The PAR-dependent system was 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-sensitive and KCN-resistant and showed a relatively high threshold irradiance for its activation; its activity was most prominent at moderate to high irradiances. The blue-light-dependent photosystem was KCN-sensitive, was active at low irradiances, and interacted with the PAR-dependent photosystem at high blue irradiances. Stomatal opening in darkness, caused by CO2-free air, fusicoccin or high KCl concentrations, was KCN-sensitive and DCMU-resistant. These data indicate that stomatal opening in darkness depends on oxidative phosphorylation for the supply of high-energy equivalents driving proton extrusion. Light-dependent stomatal opening appears to require photophosphorylation from guard-cell chloroplasts and the activation of the blue-light photosystem which could rely either on oxidative phosphorylation or a specific, membrane-bound electron-transport carrier.

Rising atmospheric CO2 concentrations may lead to increased water availability because the water use efficiency of photosynthesis (WUE) increases with CO2 in most plant species. This should allow the extension of afforestation activities into drier regions. Using eddy flux, physiological and inventory measurements we provide the first quantitative information on such potential from a 35‐year old afforestation system of Aleppo pine (Pinus halepensis Mill.) at the edge of the Negev desert. This 2800 ha arid‐land forest contains 6.5 ± 1.2 kg C m−2, and continues to accumulate 0.13–0.24 kg C m−2 yr−1. The CO2 uptake is highest during the winter, out of phase with most northern hemispheric forest activity. This seasonal offset offers low latitude forests ∼10 ppm higher CO2 concentrations than that available to higher latitude forests during the productive season, in addition to the 30% increase in mean atmospheric CO2 concentrations since the 1850s. Expanding afforestation efforts into drier regions may be significant for C sequestration and associated benefits (restoration of degraded land, reducing runoff, erosion and soil compaction, improving wildlife) because of the large spatial scale of the regions potentially involved (ca. 2 × 109 ha of global shrub‐land and C4 grassland). Quantitative information on forest activities under dry conditions may also become relevant to regions predicted to undergo increasing aridity.

Summary• This study explored possible advantages conferred by the phase shift between leaf phenology and photosynthesis seasonality in a semi-arid Pinus halepensis forest system, not seen in temperate sites.• Leaf-scale measurements of gas exchange, nitrogen and phenology were used on daily, seasonal and annual time-scales.• Peak photosynthesis was in late winter, when high soil moisture, mild temperatures and low leaf vapour pressure deficit (D L ) allowed high rates associated with high water-and nitrogen-use efficiencies. Self-sustained new needle growth through the dry and hot summer maximized photosynthesis in the following wet season, without straining carbon storage. Low rates of water loss were associated with increasing sensitivity of stomatal conductance (g s ) to soil moisture below a relative extractable water (REW) of 0.4, and decreased g s sensitivity to D L below REW of approx. 0.2. This response was captured by the modified Ball-Berry (Leuning) model.• While most physiological parameters and responses measured were typical of temperate pines, the photosynthesis-phenological phasing contributed to high productivity under warm-dry conditions. This contrasts with reported effects of short-term periodical droughts and could lead to different predictions of the effect of warming and drying climate on pine forest productivity.

Abscisic acid (ABA), a plant hormone whose production is stimulated by water stress, reduces the apertures of stomatal pores in the leaf surface, thereby lessening transpirational water loss. It has been thought that inhibition of stomatal opening and promotion of stomatal closure by ABA are initiated by the binding of extracellular ABA to a receptor located in the guard-cell plasma membrane. However, in the present research, we employ three distinct experimental approaches to demonstrate that ABA can act from within guard

Adventitious roots of ‘Beauregard’ and ‘Georgia Jet’ sweetpotato were observed and anatomically characterized over a period of 60 days of storage root development. The majority of ‘Beauregard’ and ‘Georgia Jet’ adventitious roots sampled at 5 to 7 days after transplanting (DAT) possessed anatomical features (five or more protoxylem elements) associated with storage root development. The majority of ‘Beauregard’ (86%) and ‘Georgia Jet’ (89%) storage roots sampled at 60 to 65 DAT were traced directly to adventitious roots extant at 5 to 7 DAT. The two varieties, however, differed in the timing in which regular and anomalous cambia were formed. Regular vascular cambium development, i.e., initiation and completion, was observed in both varieties at 19 to 21 DAT. Formation of complete regular vascular cambium was negligible for ‘Beauregard’ (4%) in comparison with ‘Georgia Jet’ (32%) at 26 to 28 DAT. However, anomalous cambia development adjacent to xylem elements was greater in ‘Beauregard’ (30%) in comparison with ‘Georgia Jet’ (13%). Nearly 40% to 50% of samples in both varieties showed extensive lignification in the stele region. At 32 to 35 DAT, 62% to 70% of the adventitious roots for both varieties had either been initiated (developed anomalous cambium) or were lignified. The remaining adventitious roots showed intermediate stages of vascular cambium development. The adventitious root count increased up to 19 to 21 DAT and then remained constant up to 32 to 35 DAT. These accumulated results suggest that the initial stages of adventitious root development are critical in determining storage root set in sweetpotato.

Co-localization of polyphenols and peroxidase activity was demonstrated in epidermal glands of the waterlily (Nymphaea) by histochemistry. Total phenols, tannins and peroxidase activity were determined quantitatively in plant extracts. Polyphenols were partially identified and were found to consist mainly of hydrolyzable tannins, gallic and tannic acid derivatives. Nymphaea polyphenols were shown to chelate Cr, Hg, and Pb in vitro, and Cd-binding by polymerized polyphenols was demonstrated in leaves exposed to Cd in vivo. Both polyphenols and peroxidases were found at very high constitutive levels, which were not induced or altered by external conditions, such as light and heavy-metal stress. It is suggested that the polymerization of polyphenols by peroxidases, enhanced after heavy-metal uptake and detoxification, is responsible for the binding of heavy metals in Nymphaea epidermal glands.

Ca2 (0.1-1.0 millimolar) accelerated dark-induced stomatal closure and reduced stomatal apertures in the light in epidermal peels of Commelina communis L. In contrast, ethyleneglycol-bis4(8-aminoethyl ether) N,N'tetraacetic acid (EGTA) (2 millimolar) a Ca2" chelator, prevented closure in the dark and accelerated opening in the light. EGTA did not promote significant opening in the dark. It is therefore concluded that EGTA does not increase ion uptake into guard cells, but rather prevents ion efflux. Addition of EGTA to incubating solutions with 10 millimolar KCI resulted in steady state apertures of 15.6 micrometers, whereas in the absence of EGTA similar apertures required 55 millimolar KCI and 150 millimolar KCI was needed in the presence of 1 millimolar CaC12.The results demonstrate the importance of Ca2' in the regulation of stomatal closure and point to a role of Ca2" in the regulation of K' efflux from stomatal guard cells.