Association between winter anthocyanin production and drought stress in angiosperm evergreen species

Leaves of many evergreen angiosperm species turn red under high light during winter due to the production of anthocyanin pigments, while leaves of other species remain green. There is currently no explanation for why some evergreen species exhibit winter reddening while others do not. Conditions associated with low leaf water potentials (Ψ) have been shown to induce reddening in many plant species. Because evergreen species differ in susceptibility to water stress during winter, it is hypothesized that species which undergo winter colour change correspond with those that experience/tolerate the most severe daily declines in leaf Ψ during winter. Six angiosperm evergreen species which synthesize anthocyanin in leaves under high light during winter and five species which do not were studied. Field Ψ, pressure/volume curves, and gas exchange measurements were derived in summer (before leaf colour change had occurred) and winter. Consistent with the hypothesis, red-leafed species as a group had significantly lower midday Ψ in winter than green-leafed species, but not during the summer when all the leaves were green. However, some red-leafed species showed midday declines similar to those of green-leafed species, suggesting that low Ψ alone may not induce reddening. Pressure–volume curves also provided some evidence of acclimation to more negative water potentials by red-leafed species during winter (e.g. greater osmotic adjustment and cell wall hardening on average). However, much overlap in these physiological parameters was observed as well between red and green-leafed species, and some of the least drought-acclimated species were red-leafed. No difference was observed in transpiration (E) during winter between red and green-leaved species. When data were combined, only three of the six red-leafed species examined appeared physiologically acclimated to prolonged drought stress, compared to one of the five green-leafed species. This suggests that drought stress alone is not sufficient to explain winter reddening in evergreen angiosperms

WATER STRESS-INDUCED DIURNAL-VARIATIONS IN LEAF WATER RELATIONS, STOMATAL CONDUCTANCE, SOLUBLE SUGARS, LIPIDS AND ESSENTIAL OIL CONTENT OF ORIGANUM-MAJORANA L

Diurnal changes in relative water content, water relations, stomatal conductance, soluble sugars and total lipid content were measured on potted plants of Origanum majorana L. under soil moisture deficit. Much of the drought tolerance of Origanum is due to the ability of leaves to maintain turgor potentials at levels conducive to growth and stomatal conductance. Diurnally, leaf turgor was maintained through decreasing leaf solute potential. Solute accumulation was observed, even though relative water content (RWC) was found to be higher than 60%. Combined data, of RWC and PSI-leaf measurements, indicated that leaves of plants experienced in soil water content (SWC) almost-equal-to 1.5% required less water to recover from water stress than leaves of plants experienced in SWC almost-equal-to 15%. Essential oil content, total lipids and leaf dry weight were increased as soil moisture deficit was increased. Since leaf elongation was retarded by water stress, it is suggested that dividing cells failed to subsequently enlarge because of the water stress

Free Proline Accumulation in Sapwood, Bark and Leaves of Three Evergreen Sclerophylls and a Comparison with an Evergreen Conifer

Free proline content was investigated in sapwood, bark and foliage of Ceratonia siliqua, Laurus nobilis, Myrtus communis and Pinus halepensis throughout a 12-month period. Free proline concentration in leaves and needles peaked during the drought and cold periods, respectively, then declined prior to the flushing of the new foliage; the minimum values coincided with the expansion of the young foliage. The results indicate that proline was neither translocated during stress periods, nor accumulated in turgid foliage. In the bark and sapwood of the four species examined, free proline content was generally lower compared with that of the foliage, but the seasonal trends were similar. Thus, free proline accumulation in sapwood and bark decreased during the main and secondary growth periods. © 1992, Gustav Fischer Verlag, Stuttgart. All rights reserved

Endosperm dormancy breakage in olive seeds

Seeds of Olea europaea L. ssp. oleaster Hoffm. and Link freed from the sclerous endoearp and incubated in water at 15 or 25°C in darkness or in 12:12 h white light:dark conditions, did not germinate, due to dormancy imposed by the endosperm. Seeds also did not germinate when incubated in abscisic acid, gibberellic acid, kinetin or zeatin in darkness and at cither 15 or 25°C. SAN 9789 |4‐chloro‐5‐(methylamine)‐2‐(a,a,a‐trifluoro‐m‐tolyl)‐3‐(2H)‐pyridazmone] did not promote germination at 15°C but it did to a 75% level at 25°C. This promoting effect of SAN was counteracted by abscisic acid. Cultures of naked embryos grew equally well in the presence or absence of SAN 9789. 6‐Benzylaminopurine promoted whole seed germination to a 15% level. Copyright © 1984, Wiley Blackwell. All rights reserve

Endosperm dormancy breakage in olive seeds

Seeds of Olea europaea L. ssp. oleaster Hoffm. and Link freed from the sclerous endoearp and incubated in water at 15 or 25°C in darkness or in 12:12 h white light:dark conditions, did not germinate, due to dormancy imposed by the endosperm. Seeds also did not germinate when incubated in abscisic acid, gibberellic acid, kinetin or zeatin in darkness and at cither 15 or 25°C. SAN 9789 |4‐chloro‐5‐(methylamine)‐2‐(a,a,a‐trifluoro‐m‐tolyl)‐3‐(2H)‐pyridazmone] did not promote germination at 15°C but it did to a 75% level at 25°C. This promoting effect of SAN was counteracted by abscisic acid. Cultures of naked embryos grew equally well in the presence or absence of SAN 9789. 6‐Benzylaminopurine promoted whole seed germination to a 15% level. Copyright © 1984, Wiley Blackwell. All rights reserve