Photosynthetic Characteristics of Avocado Leaves

Liu, X.; Mickelbart, Michael V.; Robinson, Paul; Hofshi, Reuben; Arpaia, Mary Lu

doi:10.17660/actahortic.2002.575.103

Cited by 9 publications

(6 citation statements)

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“…Expanding leaves remain sinks for up to 1 month until they reach about 70% to 80% of full expansion (Schaffer et al, 1991), and stomata do not become fully functional until leaves attain 90% of full expansion (Scholefield and Kriedemann, 1979). However, shoots also retain old leaves through several flushes, and leaves from the previous season contribute significantly to total plant carbon gain (Liu et al, 2002), with photosynthesis rates up to 50% of those in new, fully expanded leaves (Heath et al, 2005). These properties offer an array of opportunities for new research into the concurrent operation of the two xanthophyll cycles.…”

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confidence: 99%

De Novo Synthesis and Degradation of Lx and V Cycle Pigments during Shade and Sun Acclimation in Avocado Leaves

2008

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The photoprotective role of the universal violaxanthin cycle that interconverts violaxanthin (V), antheraxanthin (A), and zeaxanthin (Z) is well established, but functions of the analogous conversions of lutein-5,6-epoxide (Lx) and lutein (L) in the selectively occurring Lx cycle are still unclear. We investigated carotenoid pools in Lx-rich leaves of avocado (Persea americana) during sun or shade acclimation at different developmental stages. During sun exposure of mature shade leaves, an unusual decrease in L preceded the deepoxidation of Lx to L and of V to A+Z. In addition to deepoxidation, de novo synthesis increased the L and A+Z pools. Epoxidation of L was exceptionally slow, requiring about 40 d in the shade to restore the Lx pool, and residual A+Z usually persisted overnight. In young shade leaves, the Lx cycle was reversed initially, with Lx accumulating in the sun and declining in the shade. De novo synthesis of xanthophylls did not affect a-and b-carotene pools on the first day, but during long-term acclimation a-carotene pools changed noticeably. Nonetheless, the total change in a-and b-branch carotenoid pools was equal. We discuss the implications for regulation of metabolic flux through the a-and b-branches of carotenoid biosynthesis and potential roles for L in photoprotection and Lx in energy transfer to photosystem II and explore physiological roles of both xanthophyll cycles as determinants of photosystem II efficiency.It has long been recognized that photosynthesis in plants must resolve two conflicting requirements, the need to ramp up maximum light-harvesting efficiency in dim light and to wind back to lower efficiency when light is in excess, in order to maintain high rates of growth and productivity in varying light environments (Björkman, 1981;Pearcy, 1990). A wealth of research has established that plants adjust through an array of morphological and molecular events that confer photoprotection, mitigate and repair photoinactivation of PSII, and facilitate acclimation of the photosynthetic apparatus over different time scales in response to variable light regimes in wild plants, crops, and algae (Osmond et al., 1999; DemmigAdams et al., 2006). In the context of the light reactions, low light acclimation optimizes light harvesting and energy transfer to the photosystems, particularly PSII, via enlarged functional antennae, accumulation of accessory light-harvesting pigments, and down-regulation of unnecessary competing photoprotective processes.High light acclimation involves increased photoprotection and photorepair, downsized antennae, fewer photosystems, and sometimes changes in the PSI to PSII stoichiometry (Osmond et al., 1999;Fö rster et al., 2005). Along with their function in energy transfer to the photosynthetic reaction centers as accessory pigments to chlorophylls, the xanthophyll pigments violaxanthin (V), antheraxanthin (A), and zeaxanthin (Z) play a central role in these transformations of the photosynthetic apparatus, especially in thermal energy dissipation and detoxificat...

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confidence: 99%

De Novo Synthesis and Degradation of Lx and V Cycle Pigments during Shade and Sun Acclimation in Avocado Leaves

2008

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“…Las condiciones agroclimáticas de la zona productora de aguacates que comprende los municipios de Tepic y Xalisco, Nayarit, permiten el desarrollo exitoso de los árboles, sin peligro de temperaturas limitantes, pues, rara vez se presentan temperaturas extremas por largos periodos, menores de 10°C y por arriba de 38°C que puedan limitar los procesos fotosintéticos conducentes a la acumulación de carbohidratos, como ha sido demostrado en California (Liu et al, 2002) o en Nueva Zelanda (Mandemaker, 2007a). Al respecto, Mandemaker (2007a, b) señala que para lograr incrementos en los rendimientos de fruto, se requiere de un mayor entendimiento de la fisiología del aguacate, particularmente, el proceso fotosintético, donde sea posible establecer las épocas con mayores tasas de fijación de CO 2 y con-secuentemente mayor acumulación de carbohidratos.…”

Section: Introductionunclassified

“…En climas cálidos como el de Florida y California, las temperaturas alcanzan su nivel máximo durante el verano que limita el rendimiento fotosintético. La fotosíntesis neta se redujo a cerca de cero en California en 'Hass' cultivado en el campo cuando la temperatura de la hoja estuvo entre 35 a 40°C; esto estuvo fuertemente correlacionado con la reducción en la conductancia estomatal (Liu et al, 2002). Se ha encontrado que la fotosíntesis puede ser mantenida al 33 % de sus niveles máximos, a temperaturas por arriba de 40°C (Scholefield et al, 1980;Whiley y Schaffer, 1994).…”

Section: Introductionunclassified

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Seasonal variation of photosynthesis and some physiological related parameters were studied on 'Hass', 'Colin V-101' and Rincon avocado cultivars under the semiwarm subhumid climate of the Matatipac Valley, Nayarit. In each of six sampling dates, five mature leaves were measured in each of five trees per cultivar. The first measurement was made the end of the summer (21 Sept. 2002), two readings in the fall (20 Oct. and 20 Nov. 2002), two in the winter (22 Jan. and 23 Feb. 2003), and one at the beginning of the spring (30 Mar. 2003). Seasonal dispersion of the net photosynthesis rate (A) in the three avocado cultivars had a similar distribution pattern through the year. At the end of summer the rate of A was low (18.45 mmol CO 2 m-2 s-1), then showed a slight increase at the beginning of autumn (20.22 mmol CO 2 m-2

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“…At temperatures below 15 °C and above 40 °C, photosynthetic rates declined by approximately 33% (Scholefield et al, 1980 from > 14 °C to < 10 °C. Liu et al (2002) found that 'Lamb Hass' had greater CO 2 assimilation than 'Hass' in summer and autumn but not spring, and these differences were associated with higher chlorophyll concentrations of 'Lamb Hass' leaves. These results support the likelihood that varietyspecific responses to temperature in the current study would have influenced root: shoot ratio results.…”

Section: Main Discussionmentioning

confidence: 85%

“…Yet evidence suggests that they are net producers (ie. source rather than sink) of carbon slightly earlier, at 20-24 days after bud break (Liu et al, 2002). A young avocado plant with no seed source from which energy stores may be drawn upon is reliant upon the photosynthetic capabilities of source leaves for further growth and maturation.…”

Section: Main Discussionmentioning

confidence: 99%

Evaluation of phytophthora root rot resistance in avocado

Neilsen¹

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Avocado trees (Persea americana) affected by Phytophthora root rot caused by Phytophthora cinnamomi produce copious amounts of small, poor quality fruit and without intervention, affected trees eventually die. Current management practices involve an integrated approach to disease management, including planting on well-draining soil with a high total cation exchange capacity, application of organic mulch, carefully monitored organic and inorganic nutrition, phosphonate applications and the use of tolerant rootstock varieties. Selection of rootstocks in breeding programs is a time consuming process involving extensive glasshouse and field screening but little is understood about the mechanisms underlying tolerance in elite selections. The overall aim of the research described in this thesis was to identify phenotypic differences across a range of avocado rootstock varieties with varying degrees of resistance/ susceptibility that may be associated with known field susceptibility.The first hypothesis tested in this thesis is that field resistant rootstock varieties have greater root regenerative ability than susceptible varieties. This hypothesis was tested using a glasshouse study of inherent root growth of seedlings as well as an inoculation study to investigate root system health and wilting in response to infection by P. cinnamomi. To investigate whether inherent root growth correlates with known field susceptibility of seedling rootstock varieties, a 2-pot root regeneration system was successfully developed and varietal differences in root: shoot ratio across nine seedling avocado varieties assessed. Seedling 'Hass' produced the greatest amount of feeder roots relative to the surface area of mature leaves, although overall differences between seedling varieties were not significant. The main finding of the glasshouse root growth studies was that there were no strong indications that inherent root growth and root system necrosis correlated with known field susceptibility.The second hypothesis tested was whether increased surface feeder root growth of mature trees and other tree physiology attributes such as stored non-structural starch, yield, tree health and growth measurements such as tree height and canopy volume have any association with known field susceptibility. At one experimental site, feeder root growth of mature trees measured over two seasons was not significantly different between rootstocks 'Dusa' and 'SHSR-04' and no significant differences or associations were found in stored starch, tree health, yield or tree growth parameters.At the second experimental site, there were also no significant differences detected in feeder root growth of rootstock varieties. Significant differences in tree physiology were detected among rootstocks with 'Velvick' having the strongest determinate vegetative growth measured and the highest level of stored non-structural starch, although it wasn't significantly higher than fieldsusceptible 'Reed'. Overall, results of field studies at both sites indicated that t...

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Photosynthetic Characteristics of Avocado Leaves

Cited by 9 publications

References 0 publications

De Novo Synthesis and Degradation of Lx and V Cycle Pigments during Shade and Sun Acclimation in Avocado Leaves

De Novo Synthesis and Degradation of Lx and V Cycle Pigments during Shade and Sun Acclimation in Avocado Leaves

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Evaluation of phytophthora root rot resistance in avocado

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