[Show abstract][Hide abstract] ABSTRACT: Knowledge of ripeness and regulation of postharvest processes is an important tool to prevent loss of commercial value in both fruit and cut flower markets. The joint analysis of hormones and vitamin E levels can reveal complex interactions between hormones and oxidative stress as key regulators of postharvest processes. Profiling of both groups of metabolic compounds was performed during the ripening of non-climacteric fruits (red raspberry, Rubus idaeus L.) and senescence of ethylene-insensitive flowers (Dutch Iris, Iris x hollandica L.). After an initial extraction of the sample, without further purification steps, the hormonal profile was analyzed by UPLC-MS/MS and vitamin E levels were measured by HPLC. This methodological approach was very fast and had enough sensitivity for the analysis of small samples. Raspberry fruit maturation was characterized by a decline of cytokinin levels [zeatin, zeatin riboside, 2-isopentenyl adenine, and isopentenyl adenosine (Z, ZR, 2-iP, and IPA, respectively)] and gibberellins (GA1 in particular). Exogenous application of ABA prevented δ-tocopherol loss during fruit ripening. Iris floral senescence was also under strict hormonal control, also mediated by cytokinins and gibberellins. Z, ZR, 2-iP, GA9, and GA24 levels decreased in inner tepals, whereas the level of IPA decreased in style-merged-to-stigma tissues, thus suggesting tissue-specific roles for different hormones. α-Tocopherol levels decreased during senescence of inner tepals, hence suggesting enhanced oxidative stress. In conclusion, the rapid and sensitive hormonal and vitamin E profiling presented here can help in understanding the key physiological processes underlying fruit ripening and floral senescence.
[Show abstract][Hide abstract] ABSTRACT: In addition to floral senescence and longevity, the control of leaf senescence is a major factor determining the quality of several cut flowers, including Lilium, in the commercial market. To better understand the physiological process underlying leaf senescence in this species, we evaluated: (i) endogenous variation in the levels of phytohormones during leaf senescence, (ii) the effects of leaf darkening in senescence and associated changes in phytohormones, and (iii) the effects of spray applications of abscisic acid (ABA) and pyrabactin on leaf senescence. Results showed that while gibberellin 4 (GA(4)) and salicylic acid (SA) contents decreased, that of ABA increased during the progression of leaf senescence. However, dark-induced senescence increased ABA levels, but did not affect GA(4) and SA levels, which appeared to correlate more with changes in air temperature and/or photoperiod than with the induction of leaf senescence. Furthermore, spray applications of pyrabactin delayed the progression of leaf senescence in cut flowers. Thus, we conclude that (i) ABA plays a major role in the regulation of leaf senescence in Lilium, (ii) darkness promotes leaf senescence and increases ABA levels, and (iii) exogenous applications of pyrabactin inhibit leaf senescence in Lilium, therefore suggesting that it acts as an antagonist of ABA in senescing leaves of cut lily flowers.
[Show abstract][Hide abstract] ABSTRACT: Sugars are generally used to extend the vase life of cut flowers. Such beneficial effects have been associated with an improvement of water relations and an increase in available energy for respiration by floral tissues. In this study we aimed at evaluating to what extent (i) endogenous levels of sugars in outer and inner tepals, androecium and gynoecium are altered during opening and senescence of lily flowers; (ii) sugar levels increase in various floral tissues after sucrose addition to the vase solution; and (iii) sucrose addition alters the hormonal balance of floral tissues. Results showed that endogenous glucose levels increased during flower opening and decreased during senescence in all floral organs, while sucrose levels increased in outer and inner tepals and the androecium during senescence. Sucrose treatment accelerated flower opening, and delayed senescence, but did not affect tepal abscission. Such effects appeared to be exerted through a specific increase in the endogenous levels of sucrose in the gynoecium and of glucose in all floral tissues. The hormonal balance was altered in the gynoecium as well as in other floral tissues. Aside from cytokinin and auxin increases in the gynoecium; cytokinins, gibberellins, abscisic acid and salicylic acid levels increased in the androecium, while abscisic acid decreased in outer tepals. It is concluded that sucrose addition to the vase solution exerts an effect on flower opening and senescence by, among other factors, altering the hormonal balance of several floral tissues.
[Show abstract][Hide abstract] ABSTRACT: Much effort has been focussed on better understanding the key signals that modulate floral senescence. Although ethylene is one of the most important regulators of floral senescence in several species, Lilium flowers show low sensitivity to ethylene; thus their senescence may be regulated by other hormones. In this study we have examined how (1) endogenous levels of hormones in various floral tissues (outer and inner tepals, androecium and gynoecium) vary throughout flower development, (2) endogenous levels of hormones in such tissues change in cut versus intact flowers at anthesis, and (3) spray applications of abscisic acid and pyrabactin alter flower longevity. Results show that floral tissues behave differently in their hormonal changes during flower development. Cytokinin and auxin levels mostly increased in tepals prior to anthesis and decreased later during senescence. In contrast, levels of abscisic acid increased during senescence, but only in outer tepals and the gynoecium, and during the latest stages. In addition, cut flowers at anthesis differed from intact flowers in the levels of abscisic acid and auxins in outer tepals, salicylic acid in inner tepals, cytokinins, gibberellins and jasmonic acid in the androecium, and abscisic acid and salicylic acid in the gynoecium, thus showing a clear differential response between floral tissues. Furthermore, spray applications of abscisic acid and pyrabactin in combination accelerated the latest stages of tepal senescence, yet only when flower senescence was delayed with Promalin. It is concluded that (1) floral tissues differentially respond in their endogenous variations of hormones during flower development, (2) cut flowers have drastic changes in the hormonal balance not only of outer and inner tepals but also of androecium and gynoecium, and (3) abscisic acid may accelerate the progression of tepal senescence in Lilium.
[Show abstract][Hide abstract] ABSTRACT: To better understand the role of ethylene signaling in plant stress tolerance, salt-induced changes in gene expression levels of ethylene biosynthesis, perception and signaling genes were measured in Arabidopsis thaliana plants exposed to 15 days of salinity. Among the genes analyzed, EIN3 showed the highest expression level increase under salt stress, suggesting a key role for this ethylene-signaling component in response to salt stress. Therefore, we analyzed the salt stress response over 15 days (by adding 100 mM NaCl to the nutrient solution) in the ein3-1 mutant compared to the wild-type (Col-0) in terms of growth, oxidative stress markers (lipid peroxidation, foliar pigments and low-molecular-weight antioxidants) and levels of growth- and stress-related phytohormones (including cytokinins, auxins, gibberellins, abscisic acid, jasmonic acid and salicylic acid). The ein3-1 mutant grew similarly to wild-type plants both under control and salt stress conditions, which was associated with a differential time course evolution in the levels of the cytokinins zeatin and zeatin riboside, and the auxin indole-3-acetic acid between the ein3-1 mutant and the wild-type. Despite showing no signs of physiological deterioration under salt stress (in terms of rosette biomass, leaf water and pigment contents, and PSII efficiency) the ein3-1 mutant showed enhanced lipid peroxidation under salt stress, as indicated by 2.4-fold increase in both malondialdehyde and jasmonic acid contents compared to the wild-type. We conclude that, at moderate doses of salinity, partial insensitivity to ethylene might be compensated by changes in endogenous levels of other phytohormones and lipid peroxidation-derived signals in the ein3-1 mutant exposed to salt stress, but at the same time, this mutant shows higher oxidative stress under salinity than the wild-type.
[Show abstract][Hide abstract] ABSTRACT: Although the biosynthesis and function of tocopherols (vitamin E) in leaves and seeds have been studied in detail, their occurrence within other plant organs/tissues is still poorly understood. In an attempt to better understand the occurrence and possible functions of tocopherols in flowers, we measured the concentrations of the four tocopherol homologues in floral organs of Lilium (including the gynoecium, androecium, and inner and outer tepals), and evaluated their variations in tepals of cut, senescing flowers (artificial senescence) compared to controls (natural senescence). Results showed that flowers accumulated α-tocopherol at significant amounts, while γ-tocopherol was present at much lower concentrations. The androecium was the organ showing the highest amounts of tocopherols, with a specific accumulation in the pollen, while tocopherols were not present in the gynoecium. Inner and outer tepals also contained significant amounts of α- and γ-tocopherol, whose levels increased during senescence. α-Tocopherol increased in both outer and inner tepals earlier and to a higher extent during senescence of cut flowers than in controls. The lowest concentrations of tocopherols were found at the beginning of tepal development (in green tepals), while the highest concentrations were found in chlorophyll-free, senescing tepals, especially in cut flowers. It is concluded that (i) tocopherols accumulate in outer and inner tepals, and in the androecium of Lilium flowers, particularly in the pollen, and (ii) tocopherols increase with the progression of tepal senescence, and most particularly in cut flowers, which show advanced senescence (reduced longevity).
[Show abstract][Hide abstract] ABSTRACT: Acclimation of photosynthetic light reactions to daily changes in solar radiation requires adjustments in photosystem II photochemistry and may be affected by environmental stresses, such as drought. In this study, we examined the effects of a short-term, severe water deficit on diurnal variations in photosystem II photochemistry, photoprotective compounds (tocopherols and carotenoids, including the xanthophyll cycle) and stress-related phytohormones (abscisic acid and salicylic acid) in the CAM plant, Aptenia cordifolia L. f. Schwantes. Violaxanthin was rapidly converted to zeaxanthin under high light, the de-epoxidation state of the xanthophyll cycle reaching maximum levels of 0.95 at midday in irrigated plants. Under a higher photoprotective demand caused by water deficit, plants showed significant increases in abscisic acid and γ-tocopherol levels, which were followed by decreases in β-carotene and the Fv/Fm ratio at later stages of stress. Decreases in this ratio below 0.70 correlated with sustained increases in the de-epoxidation state of the xanthophyll cycle, which kept above 0.90 at night after 15 days of water deficit. In contrast to abscisic acid, salicylic acid levels kept constant under water deficit and showed a sharp decrease during the day both under irrigated and water stress conditions. We conclude that the CAM plant, A. cordifolia showed several strategies of acclimation to short-term water deficit, including abscisic acid and γ-tocopherol accumulation, as well as sustained increases in the de-epoxidation state of the xanthophyll cycle, which was tightly coupled to daily variations in photosystem II photochemistry. The differential accumulation of tocopherol homologues under water deficit and the diurnal fluctuations of salicylic acid levels in this CAM plant will also be discussed.