Summary• Perturbations of the source-sink balances were performed in field-grown coffee (Coffea arabica) trees to investigate the possible role of carbohydrates in feedback regulation of photosynthesis.• Four treatments were applied at the whole-plant level: (i) complete defruiting and maintenance of the full leaf area, (ii) the half crop load and full leaf area, (iii) the full crop load and full leaf area and (iv) the full crop load and half leaf area. Sampling and measurements were performed twice during the phase of dry matter accumulation of fruits. Gas exchange, chlorophyll a fluorescence, carbon isotope labelling and steady-state metabolite measurements were assessed in source leaves.• The average rate of net photosynthetic rate (A) and stomatal conductance (g s ) were larger (> 50%), and carbon isotope composition ratio was lower, in trees with a full crop load and half leaf area than in defruited trees, with individuals of the other two treatments showing intermediate values. However, differences in A seem unlikely to have been caused either by photochemical impairments or a direct end-product-mediated feedback down-regulation of photosynthesis.• It is proposed that the decreased A in defruited coffee trees was independent of carbon metabolism and was rather directly related to a lower CO 2 availability coupled to lower g s .

Limitations to photosynthesis were explored in leaves from four canopy positions of field-grown, unshaded coffee (Coffea arabica L.), a tropical tree species classified as shade-obligatory. Overall, compared to shade (lower) leaves, sun (upper) leaves had higher net carbon assimilation rate (A) (4.5 against 2.0 micromol m(-2)s(-1) at most) associated with higher electron transport rate (due to a greater irradiance availability) but unrelated to stomatal and mesophyll conductances, which were similar regardless of leaf position. Neither physiological variable directly involved with photosynthetic carbon gain nor those involved with light capture were able to adjust themselves to match the capacity of the photosynthetic machinery to the light supply. We concluded that: (i) there was no major difference in photosynthetic capacity between sun and shade leaves; (ii) the intrinsic low A in coffee was greatly associated with remarkable low diffusive limitations rather than with biochemical or photochemical constraints; and (iii) morphological (e.g., variations in specific leaf area and leaf inclination) or anatomical plasticity should be of greater acclimative value than physiological plasticity as a mean of coffee leaves to respond to changing irradiance.

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RESUMOEste trabalho teve por objetivo caracterizar a atividade potencialmente alelopática de óleos essenciais de pimenta longa (Piper hispidinervium C. DC.) e oriza (Pogostemon heyneanus Benth) e analisar, comparativamente, seus efeitos alelopáticos. Óleos essenciais obtidos foram preparados em concentrações de 0,25, 0,5 e 1,0%, tendo como eluente o éter metílico, e testados sobre a germinação de sementes, desenvolvimento da radícula e do hipocótilo das plantas daninhas de área de pastagens cultivadas, malícia (Mimosa pudica) e mata-pasto (Senna obtusifolia). Os óleos das duas espécies evidenciaram atividade alelopática em intensidades que variaram em função da concentração do óleo, da espécie doadora, da planta receptora e do fator da planta analisado. A germinação das sementes foi o fator mais intensamente inibido pelos óleos. As intensidades das inibições estiveram positivamente associadas à concentração, com inibições máximas verificadas a 1,0%. Malícia foi à espécie receptora mais sensível aos efeitos do óleo. Comparativamente, o óleo essencial da pimenta longa revelou maior potencial para inibir a germinação e o desenvolvimento das duas plantas receptoras, notadamente em relação à germinação de sementes, quando as diferenças foram mais marcantes. Os resultados foram atribuídos à composição química dos óleos, especialmente em relação à presença de monoterpenos, monoterpenos oxigenados e sesquiterpenos.PALAVRAS-CHAVE: Alelopatia, Inibição, Monoterpenos, Sesquiterpenos. Potentially allelopathic effects of the essential oils of Piper hispidinervium C. DC. and Pogostemon heyneanus (Benth) on weeds ABSTRACTThis study aimed to characterize the potential allelopathic activity of essential oils of pimenta longa (Piper hispidinervium C. DC.) and oriza (Pogostemon heyneanus Benth), and to examine, comparatively, their allelopathic effects. Essential oils obtained were prepared at concentrations of 0.25%, 0.5% and 1.0%, with ether methanol as eluent, and tested upon the germination of seeds and the development of the radicle and the hypocotyl of the weeds of cultivated grassland areas, malícia (Mimosa pudica) and mata-pasto (Senna obtusifolia). Depending on their concentrations, oils of the two species showed intensities of allelopathic activity on the donor species, on the receptor plant and on the examined plant factor. The germination of seeds was the factor most strongly inhibited by the oils. The intensities of inhibitions were positively related to the concentration, with the maximum inhibitions verified at 1%. Mimosa pudica was the receptor species most sensitive to the effects of oil. In comparison, the essential oil of Piper hispidinervium showed a higher potential for inhibiting the germination and development of the two receptor plants, notably in relation to the germination of seeds, when the differences were more striking. The results were attributed to the chemical composition of oils, especially in relation to the presence of monoterpenes, oxygenated monoterpenes and sesquiterpenes.

There is still no consensus on the true origin of fatal yellowing, one of the most important diseases affecting oil palm (Elaeis guineensis Jacq.) plantations. This study involved two-dimensional liquid chromatography coupled with tandem mass spectrometry (2D-UPLC-MSE) analyses to identify changes in protein profiles of oil palms affected by FY disease. Oil palm roots were sampled from two growing areas. Differential accumulation of proteins was assessed by comparing plants with and without symptoms and between plants at different stages of FY development. Most of the proteins identified with differential accumulation were those related to stress response and energy metabolism. The latter proteins include the enzymes alcohol dehydrogenase and aldehyde dehydrogenase, related to alcohol fermentation, which were identified in plants with and without symptoms. The presence of these enzymes suggests an anaerobic condition before or during FY. Transketolase, isoflavone reductase, cinnamyl alcohol dehydrogenase, caffeic acid 3-O-methyltransferase, S-adenosylmethionine synthase, aldehyde dehydrogenase and ferritin, among others, were identified as potential marker proteins and could be used to guide selection of FY-tolerant oil palm genotypes or to understand the source of this anomaly. When comparing different stages of FY, we observed high accumulation of alcohol dehydrogenase and other abiotic stress related-proteins at all disease stages. On the other hand, biological stress-related proteins were more accumulated at later stages of the disease. These results suggest that changes in abiotic factors can trigger FY development, creating conditions for the establishment of opportunistic pathogens.

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