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Overwintering evergreen trees in boreal regions continuously convert absorbed light energy into heat through a process known as sustained thermal dissipation. To better understand this mechanism, this study examined the alterations in the photosynthetic apparatus and transcriptomes of yew (Taxus cuspidata) leaves throughout the year, comparing sun-exposed and shaded leaves. The Y (II) parameter, conventionally used to estimate the quantum yield of photosystem II (PSII), indicated the occurrence of temperature-dependent thermal dissipation during winter. On the other hand, the levels of photosystem subunits, including the D1 subunit of the PSII reaction center, remained relatively stable year-round, indicating that typical photoinhibition is unlikely to occur. Time-resolved chlorophyll fluorescence analysis revealed that heat dissipation at the PSII antenna is prominent in winter. Winter transcriptomes are notably characterized by a predominance of Elip transcripts encoding early light-induced protein (ELIP), which constitute 20% of the total transcripts, as deduced from RNA-seq analysis. Furthermore, ELIP protein concentration increased to nearly half that of the major light-harvesting complexes. The predicted structure of ELIP includes potential chlorophyll a and carotenoid binding sites. These findings, taken together with a previous report showing ELIP capacity for energy dissipation, lead to a re-evaluation of its significant role in sustained thermal dissipation. [ABSTRACT FROM AUTHOR]

We hypothesized that anthocyanins act as a sugar-buffer and an alternative electron sink during leaf senescence to prevent sugar-mediated early senescence and photoinhibition. To elucidate the role of anthocyanin, we monitored seasonal changes in photosynthetic traits, sugar, starch and N contents, pigment composition, and gene expression profiles in leaves exposed to substantially different light conditions within a canopy of an adult fullmoon maple (Acer japonicum) tree. Enhancement of starch amylolysis accompanied by cessation of starch synthesis occurred in the same manner independent of light conditions. Leaf sugar contents increased, but reached upper limits in the late stage of leaf senescence, even though leaf anthocyanins further increased after complete depletion of starch. Sun-exposed leaves maintained higher energy consumption via electron flow than shade-grown leaves during leaf N resorption. Thus, anthocyanins accumulated in sun-exposed leaves might have a regulative role as a sugar-buffer, retarding leaf senescence, and an indirect photoprotective role as an alternative sink for electron consumption to compensate declines in other metabolic processes such as starch and protein synthesis. In this context, anthocyanins may be key substrates protecting both outer-canopy leaves (against photoinhibition) and inner-canopy leaves (via shading by outer-canopy leaves) from high light stress during N resorption. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) is a major phytohormone that regulates development and growth. Increasingly, the literature indicates that ABA enhances and inhibits a spectrum of plant responses within an hormetic-like biphasic dose-response manner. A recent extensive study on the response of a variety of Arabidopsis lines to ABA suggested the widespread occurrence of hormetic dose responses. Our independent reassessment of these data reveals the occurrence of more than 30 hormetic dose-response relationships with quantitative features fully consistent with the substantial and extensively assessed literature on plant hormesis. This analysis significantly extends earlier findings indicating that ABA mediates a broad spectrum of hormetic dose responses in plants. ABA-induced hormesis provides a novel framework for research with the potential to advance the current scientific bases of plant ecology, physiology, and toxicology and to enhance agricultural yields and productivity. Keywords: abscisic acid, adaptive response, dose-response, hormesis, preconditioning. L'acide abscissique (ABA) est une phytohormone importante qui regule le developpement et la croissance. Une litterature abondante indique que l'ABA accroit et inhibe tout un spectre de reponses chez les vegetaux en fonction de sa concentration de maniere hormetique biphasique. Une etude exhaustive recente sur la reponse d'une variete de lignees d'Arabidopsis a l'ABA suggerait que les reponses hormetiques en fonction de la concentration etaient repandues. La reevaluation de ces donnees realisee independamment par les auteurs revele la presence de plus de 30 relations dose-reponse hormetiques dont les caracteristiques quantitatives sont entierement coherentes avec les donnees substantielles et exhaustives de la litterature portant sur l'hormese chez les plantes. Cette analyse etend de maniere significative les donnees anterieures a l'effet que l'ABA medie un large spectre de reponses hormetiques chez les plantes. L'hormese induite par l'ABA fournit un nouveau cadre de recherche ayant le potentiel de faire avancer les bases scientifiques actuelles de la biologie, de la physiologie et de la toxicologie des vegetaux, et d'accroitre les rendements et la productivite en agriculture. [Traduit par la Redaction] Mots-cles : acide abscissique, reponse adaptative, dose-reponse, hormese, preconditionnement., Introduction Abscisic acid (ABA), a sesquiterpenoid, is a key phytohormone that has long been known for its capacity to affect plant development and growth (Nambara and Marion-Poll 2005; Cutler et [...]

Competition between planted seedlings and vegetation is a critical constraint affecting the survival and growth of seedlings at the initial stages of forestation. Quantitatively assessing the impact of competitive vegetation on the growth of planted seedling is vital for reduction of weeding cost. This study compared the survival and growth of potentially fast-growing hybrid larch F1 seedling (Larix gmelinii var. japonica × L. kaempferi) with Japanese larch (L. kaempferi) at three competitive levels, which were 0–50%, 50–75% and 75–100% of the seedling surface covered by vegetation after planting. When more than three-quarters of the seedling surface was covered by vegetation, the survival rate of Japanese larch dropped substantially. In contrast, hybrid larch F1 sustained a high survival of 95% despite the high covering. Annual height growth significantly decreased with increasing coverage for both species. In addition, the height growth of hybrid larch F1 was significantly higher than that of Japanese larch, whereas the difference became insignificant when more than three-quarters of the surface was covered. If the requirement for weeding is whether three-quarters of the seedling surface is covered or not with vegetation, it was determined that hybrid larch F1 did not require weeding if the seedling height attained about 170 cm in the previous fall; whereas Japanese larch needed about 200 cm. The findings imply that weeding is needed to unlock the hybrid larch F1's high growth potential, and that weeding can be accomplished more than a year earlier than with Japanese larch. [ABSTRACT FROM AUTHOR]