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The article presents various subjects discussed in the journal "Plant, Cell and Environment," published as of December 1, 1979. Some of the subjects discussed are as follows. Abscisic acid is discussed on page 325, Acid-base regulation is discussed on page 245, Albumins is discussed on page 221, Anthocyanin synthesis is discussed on page 159, Assimilate movement is discussed on page 107, Autotropic straightening is discussed on page 149, Deoxyribonucleic acid is discussed on page 199 and Electron microscopy is discussed on page 211.

Abscisic acid (ABA) is taken up by guard cells of isolated epidermata of Valerianella locusta only at low external pH values. At pH 8.0, when nearly all ABA molecules are present as the anion of ABA (ABA-), no uptake can be observed. ABA- dependent movement of stomata was tested at external pH values between 5.0 and 8.0. Independent of the external pH, ABA induced stomatal closure at all tested ABA concentrations. It is concluded that ABA need not be taken up into the cytosol of the guard cells in order to induce stomatal closure. The primary site of ABA action at the guard cell plasmalemma must be located either at the outer surface of the plasmalemma or at least be easily accessible from outside. ABA- Is as effective as undissociated ABA (ABAH). [ABSTRACT FROM AUTHOR]

A correction to the article "Abscisic acid is involved in the response of grape (Vitis vinifera L.) cv. Malbec leaf tissues to ultraviolet-B radiation by enhancing ultraviolet-absorbing compounds, antioxidant enzymes and membrane sterols," that was published in the previous issue is presented.

Abstract A new model of stomatal conductance is proposed which combines the essential features of the Ball–Berry–Leuning (BBL) and Tardieu–Davies (TD) models within a simple spatially aggregated picture of guard cell function. The model thus provides a coherent description of stomatal responses to both air and soil environments. The model also presents some novel features not included in either the BBL or TD models: stomatal sensing of intercellular (rather than leaf surface) CO2 concentration; an explanation of all three observed regimes (A, B and C) of the stomatal response to air humidity (Monteith Plant, Cell and Environment 18, 357–364, 1995); incorporation of xylem embolism; and maintenance of hydraulic homeostasis by combined hydraulic and chemical signalling in leaves (in which leaf epidermal hydraulic conductivity plays a key role). Significantly, maintenance of hydraulic homeostasis in the model does not require a direct feedback signal from xylem embolism, the predicted minimum leaf water potential being independent of xylem hydraulic conductivity. It is suggested that stomatal regulation through combined hydraulic and chemical signalling in leaves and/or roots provides a general mechanism enabling plants to maintain their water potentials above a minimum value. Natural selection of the key stomatal parameters would then set the minimum potential to a specific value determined by the most vulnerable plant process under water stress (e.g. cell growth, protein synthesis or xylem cavitation), depending on species and growth conditions. [ABSTRACT FROM AUTHOR]

Abstract Stomatal conductance, g s , responds both tothe immediate or local environment of the leaf, such as CO2 partialpressure and irradiance, and to root-sourced signals of water stress,particularly abscisic acid (ABA). Two models for the combined controlof g s were formulated and tested in sunflower(Helianthus annuus ). First, several empirical models weretested for the local control, demonstrating that the Ball–Berrymodel [Ball, Woodrow & Berry (in Progress in PhotosynthesisResearch Vol. 4, pp. 5.221–5.224: M. Nijhoff,Dordrecht, The Netherlands) 1987] is consistently amongthe most accurate. A problem of statistical non-independence inthis model is shown to be minor. The model offers regularity ofparameter values among most species and, despite an oversimplicationin representing known humidity-response mechanisms, it incorporates othersignalling loops from CO2 and assimilation. In the firstcombined model, ABA as its concentration in xylem sap, [ABA]xy ,down-regulates the slope, m , in the Ball–Berry modelby the factor g fac = exp(– β [ABA]xy ).The ABA-induced reduction in g s decreases CO2 assimilation andsurface humidity, thus appearing to induce the local-control mechanismto amplify the ABA-induced stomatal closure. In the second combinedmodel, g s is estimated as the minimum of the local(Ball–Berry) response and the product g fac g s,max ,with g s,max as a maximal unstressed conductance.Both models can predict g s from the external environmentalvariables with good accuracy (r 2 near 0·8 over20-fold variations in g s ). Further analyses showthat g s responds to humidity almost quadraticallyrather than linearly. It also responds to assimilation as a powerlaw with an exponent that is significantly less than 1. These... [ABSTRACT FROM AUTHOR]

Abstract Petioles of water-sufficient intact Vicia faba L. plants were infused with 1 µm abscisic acid (ABA) to simulate the import of root-source ABA. This protocol permitted quantitative ABA delivery, up to 300 pmol ABA over 60 min, to the leaf without ambiguities associated with perturbations in plant–water status. The ABA concentrations in whole-leaf samples and in apoplastic sap increased with the amount infused; ABA degradation was not detected. The ABA concentration in apoplastic sap was consistent with uptake of imported ABA into the leaf symplast, but this interpretation is qualified. Our focus was quantitative cellular compartmentation of imported ABA in guard cells. Unlike when leaves are stressed, the guard-cell symplast ABA content did not increase because of ABA infusion (P = 0·48; 3·0 ± 0·5 versus 4·0 ± 1·2 fg guard-cell-pair-1). However, the guard-cell apoplast ABA content increased linearly (R2 = 0·98) from -0·2 ± 0·5 to 3·1 ± 1·3 fg guard-cell-pair-1 (≈ 3·1 µm) and was inversely related to leaf conductance (R2 = 0·82). Apparently, xylem ABA accumulates in the guard-cell wall as a result of evaporation of the apoplast solution. This mechanism provides for integrating transpiration rate and ABA concentration in the xylem solution. [ABSTRACT FROM AUTHOR]