Angelos Patakas

The role of organic solute and ion accumulation in osmotic adjustment in drought-stressed grapevines

Abstract Water relations, gas exchange as well as organic solute and ion accumulation were studied in the leaves of 2-year-old grapevines (Vitis vinifera L, cv. Savatiano) grown under well watered (control) and water stress conditions. Both osmotic potential at full turgor (Π100) and at turgor loss point (Π0) decreased significantly in stressed plants compared with the control. Photosynthetic rate, and stomatal conductance were also significantly lower in stressed plants. Starch concentration decreased almost threefold in stressed plants, while there were no significant differences in sugar accumulation between the two treatments. Total inorganic ion concentration increased rapidly in stressed plants and seems to be the major component of osmotic adjustment in stressed grapevines. Thus, the energetic cost of osmotic adjustment in grapevines using inorganic ions would be expected to be much lower than for those species using organic solutes.

Water stress affects leaf anatomy, gas exchange, water relations and growth of two avocado cultivars

Two cultivars of avocado (Persea americana Mill., ‘Fuerte’ and ‘Hass’) plants, grown in 50 l containers, were studied under two irrigation regimes for 6 months in order to evaluate the growth response and leaf physiological and anatomical changes induced by moderate water stress. Irrigation was applied when soil water potential reached at � 0.03 and � 0.5 MPa for the wet and dry treatments, respectively. Leaf anatomy changed in water-stressed leaves, which could have accounted for the decreased stomatal conductance. Photosynthesis is inhibited by reducing the diffusion of CO2 to the chloroplast, both by stomatal closure and changes in mesophyll structure, which decreases the conductance to CO2 diffusion within the leaf. Predawn leaf water potential (C) declined by 0.9 MPa for ‘Fuerte’ and 1.2 MPa for ‘Hass’ after 12 days of withholding water, whereas the turgor potential (Cp) remained positive due to a decrease in the osmotic potential (Cp) in both cultivars. The reduction in osmotic potential was mainly due to dehydration and only partly related to active accumulation of solutes. Tissue elasticity seems to be the predominant physiological mechanism of drought adaptation of avocado. Growth data suggests that ‘Hass’ seems to be more affected by moderate water stress. # 2002 Elsevier Science B.V. All rights reserved.

Changes in water relations, photosynthesis and leaf anatomy induced by intermittent drought in two olive cultivars

Abstract Photosynthetic rate, water relations parameters as well as leaf anatomical characteristics were studied in two olive cultivars ( Olea europea, cv ‘Koroneiki’ and cv ‘Mastoidis’) grown under water stress conditions. No significant differences were obtained between the two cultivars concerning their ability for turgor maintenance under water stress conditions. ‘Koroneiki’ seems to maintain higher photosynthetic rates with lower values of stomatal conductance than ‘Mastoidis’, a fact that could be attributed to differentiation in leaf anatomy induced by water stress conditions. The fraction of mesophyll volume represented by intercellular air spaces as well as the surface area of mesophyll cell walls exposed to intercellular spaces was larger in ‘Koroneiki’ than in ‘Mastoidis’. The possibility of using leaf anatomical characteristics as selection factors for olive cultivars grown under drought conditions is discussed.

Leaf age effects on solute accumulation in water-stressed grapevines

Summary The effects of leaf age on water relations, organic solute, and total ion accumulation were studied in mature and immature leaves of two-year-old grapevines (Vitis vinifera L., cv. Savatiano) grown under water stress conditions. Osmotic potential at full turgor decreased significantly in leaves of stressed plants, irrespective of leaf age, indicating the occurrence of an active osmotic adjustment. The apoplastic water fraction (A) increased during leaf ontogeny in both control and stressed plants. However, the values of A were lower in stressed plants. Starch concentration decreased significantly in both mature and immature leaves during the drought cycle, while the relative proportion of monosaccharides and sucrose was markedly different in immature leaves compared to mature. The accumulation of total inorganic ions, induced by drought, was also age dependent, increasing significantly with leaf age, while there were no significant differences in total amino acids content. Inorganic ions and carbohydrates seem to be the major component of osmotic adjustment in mature and immature grapevine leaves, respectively.

Mechanisms Involved in Diurnal Changes of Osmotic Potential in Grapevines under Drought Conditions

Summary The aim of this study was the quantitative determination of the contribution of various possible mechanisms involved in diurnal changes of osmotic potential in grapevine leaves ( Vitis vinifera L., cv. Victoria ) under water stress conditions. Results of this study revealed that dehydration accounted for 36 % of the diurnal changes in osmotic potential in stressed plants. The relative contribution of changes in non-osmotic volume was negative. Net solute accumulation accounted for 73 % of the diurnal changes, indicating the occurrence of an active osmotic adjustment during the day in stressed plants. There was evidence that compounds other than sugars contributed to diurnal osmotic adjustment in stressed grapevines.

The relationships between CO2 transfer mesophyll resistance and photosynthetic efficiency in grapevine cultivars

Abstract Physiological and leaf anatomical characteristics were studied in the three grapevine (Vitis vinifera L.) cvs Athiri, Asyrtiko and Syrah grown under field conditions. Athiri and Asyrtiko exhibited higher values of photosynthetic rate and photosynthetic rate to intercellular CO2 ratio at high leaf water potential than Syrah, while there were no significant differences in stomatal conductance and chlorophyll content between the cultivars. Palisade and spongy parenchyma thickness and the fraction of the intercellular air spaces were significantly lower in Syrah. The surface of mesophyll cells exposed to the intercellular air spaces per unit leaf area was also lower in Shiraz, but there were no significant differences in the calculated value of the leaf internal CO2 gas phase resistance between the cultivars. The differences in the rate of photosynthesis might be attributed to differences in the CO2 liquid-phase resistance in the leaves.

Differences in stomatal responses and root to shoot signalling between two grapevine varieties subjected to drought

A comparative study on stomatal control between two grapevine varieties (Vitis vinifera L. cvs Sabatiano and Mavrodafni) differing in their ability for drought adaptation was conducted using 3-year-old own-rooted plants. The plants were subjected to prolonged drought stress by withholding irrigation water. The relationship between predawn water potential and maximum stomatal conductance indicated significant differences in stomatal sensitivity to drought between the two varieties. Stomatal closure occurred at higher values of predawn water potential in Sabatiano compared with Mavrodafni. No significant differences were found in plant hydraulic conductance and osmotic potential at full turgor (π100) between the two varieties. Leaf and root ABA concentrations increased more rapidly in Mavrodafni compared with Sabatiano at the beginning of the drought period. Furthermore, Mavrodafni also exhibited significantly higher xylem pH values as well as higher stomatal sensitivity to ABA and pH increase compared with Sabatiano. Results suggest that these two grapevine varieties might have evolved different strategies in order to adapt under drought conditions. In particular, the greater ability for drought adaptation in Sabatiano might be attributed to the more efficient regulation of stomatal closure. In contrast, chemical signalling in Mavrodafni seems to be the main mechanism for drought adaptation.

Effect of Iron Deficiency on Gas Exchange and Catalase and Peroxidase Activity in Citrus

Abstract The effects of iron (Fe) deficiency on catalase and peroxidase activity, net photosynthesis (Pn), stomatal conductance (g s ), plant water relations, and specific leaf weight, were studied under greenhouse conditions in two sweet orange (C. sinensis) cultivars grafted on sour orange (Citrus aurantium) and Swingle citrumelo (C. paradisi × P. trifoliata). Iron deficiency caused by the absence of Fe in the Hoagland nutrient solution reduced significantly catalase and peroxidase activity, photosynthesis (Pn), osmotic potential (Ψ π ), turgor potential (Ψ p ), and specific leaf weight, but did not influence g s and leaf water potential (Ψ L ). Iron deficiency caused by increasing concentrations of bicarbonate supplied as NaHCO3 (10 and 40 mM) in the nutrient solution reduced significantly g s , Pn, and Ψ p and increased Ψ L and Ψ π . Furthermore, remarkable differences were recorded between the various cultivars/rootstocks combinations.

An indirect method of estimating leaf area index in cordon trained spur pruned grapevines

The aim of this study was to validate an indirect method of estimating leaf area index (LAI) in cordon-trained spur-pruned grapevines. Indirect estimates were made using the LAI-2000 instrument, based on the principles of gap fraction theory. Results indicate that using an adjustment coefficient factor, this method could provide rapid and accurate estimates of LAI.

Abiotic Stress-Induced Morphological and Anatomical Changes in Plants

Plant abiotic stress responses include changes in both physiological and biochemical processes as well as in anatomical and developmental patterns. Despite the diversity in plant species and abiotic stresses, a generic “stress-induced” response at the plant anatomical level is reported which is mainly comprises three components: inhibition of cell elongation, localized stimulation of cell division, and alterations in cell differentiation status. This result in changes in anatomical characteristics of basic plants organs mainly roots, xylem, and leaves which contribute in adaptation to unfavorable environmental conditions. Taking into consideration that drought consist the most important environmental constraint to plant growth and production, this chapter refers to the holistic approach of anatomical changes at both organ and organism level under limiting soil water availability. The agronomical significance and perspectives of this stress-induced anatomical alterations are discussed.