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The light requirement and low-temperature stimulation of anthocyanin synthesis in peel of apple (Malus domestica) and pears (Pyrus communis) and the presence of anthocyanins in immature fruits are not congruent with a visual function in dispersal. We hypothesized that anthocyanins afford photoprotection to peel during low-temperature-induced light stress and that the protection is not a fortuitous side-effect of light absorption by anthocyanin. The extent of photoinhibition at harvest and after light stress treatment in pear cultivars differing in redness decreased with increasing red color on the sun-exposed sides of fruits. Green-shaded sides of the pears showed comparable levels of photoinhibition indicating that pears did not differ in their inherent photosensitivity. Apple and pear peel show considerable short-term fluctuation in redness in response to temperature, with red color increasing rapidly in response to low temperature and just as quickly fading in response to high temperature. Briefly, shading pears and apples during cold conditions for 2 days reduced the accumulation of anthocyanin and increased the photosensitivity of peel. Subsequent shading during warm conditions did not affect the accumulation of anthocyanin or the photosensitivity of peel indicating that the response at low temperature was not due to shade adaptation. The assessment of photosystem II (PSII) efficiency and quenching of chlorophyll fluorescence between 16 and 40 degrees C indicated that 'Forelle' pear peel was particularly sensitive to photostress at low temperature. The photosynthetic system in mature 'Forelle' leaves was comparatively much less sensitive to light stress at low temperature. Results support the view that anthocyanins are adaptable light screens deployed to modulate light absorption in sensitive tissues such as fruit peel in response to environmental triggers such as cold front snaps.

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We examined interrelationships between crop load, nitrogen (N), phosphorus (P), and potassium (K) uptake, and root growth in mature, alternate-bearing pistachio (Pistacia vera L.) trees. Pistachio trees bear heavy (on-year) and light (off-year) fruit crops in alternate years. Uptake and partitioning of N, P, and K among tree parts were determined during (a) spring flush (mid-March to late May), (b) nut fill (late May to early September), and (c) postharvest-leaf senescence (late September to early December). Nutrient uptake occurred primarily during nut fill in both on-year and off-year trees. In on-year trees, N and K uptake increased by 35 and 112%, respectively, during nut fill compared with off-year trees. During this period, nutrients were allocated largely to embryo development in on-year trees and to storage in perennial tissues in off-year trees. Nutrient uptake was negligible between harvest and leaf senescence. Although root growth was reduced during nut fill in on-year trees compared with off-year trees, there was no relationship between root growth and the uptake of N, P or K from the soil. Our data support the hypothesis that sink demand regulates the uptake and distribution of N, P, and K in pistachio trees.

No abstract