ABSTRACT Nasturtium (Tropaeolum majus) is an ornamental and medicinal plant that has edible flowers. Drought and salt stress decrease flower production and quality, including affecting sugar metabolism and ethylene production. Ethylene can accelerate the nasturtium senescence process, decreasing its postharvest quality. The use of polyamines, mainly spermine, may be a strategy for reducing the harmful effects of these stresses on the metabolism of sugars and phenolic compounds and for decreasing the production of ethylene, which accelerates senescence, in nasturtium flowers. Therefore, the objective here was to evaluate the role of spermine application on sugar and phenolic compounds and on ethylene production in nasturtium flowers grown under drought and salt stress. Two experiments were performed in isolation and at the same time in order to achieve this. Spermine down-regulated ethylene production and up-regulated the content of sugars and phenolic compounds on nasturtium flowers grown under drought and saline stress. Sugars and phenolic compounds down-regulated ethylene production in nasturtium flowers. Spermine can be used to mitigate the harmful effects of drought and salt stress on nasturtium flowers by increasing sugar and phenolic compounds and decreasing ethylene production. Tropaeolum majus quality process polyamines Therefore this downregulated down regulated upregulated up

Resumo: Semente de estilosantes (Stylosanthes humilis H.B.K.) é conhecida por apresentar tegumento rijo e quando recém colhida também exibe dormência fisiológica, entretanto, a natureza da coação entre o tegumento e o crescimento do embrião que determina a sua dormência é pouco conhecida. Nesse estudo, a dormência física de sementes de estilosantes não foi reduzida durante o envelhecimento natural à temperatura ambiente, em contraste com a dormência fisiológica que foi superada gradualmente durante o envelhecimento pós-colheita. Além disso, a permeabilidade do tegumento foi afetada por tratamentos de escarificação bem como por soluções de baixo pH. Juntos, esses resultados indicam que a superação da dormência física da semente é um pré-requisito para a protrusão da radícula e a dormência fisiológica das sementes de estilosantes contribui para temporização da germinação.

Abstract: Seed of Townsville stylo (Stylosanthes humilis H.B.K.) is known to exhibit a hard seed coat and when freshly harvested also show a physiological dormancy, however, the nature of the co-actions between seed coat and embryo growth that determine dormancy is poorly understood. In this study, physical dormancy of Townsville stylo seeds was not reduced during natural ageing at room temperature, in contrast to the physiological dormancy, which is gradually overcome during after-ripening. Furthermore, the permeability of seed coat was affected by scarification treatments as well as by low-pH solutions. Together, these data indicate that physical dormancy overcome of seed is prerequisite for radicle protrusion and physiological dormancy of Townsville stylo seeds contribute to its timing.

Resumo O óxido nítrico (ON) vem se destacando como estimulador do processo de germinação para muitas espécies. Há poucos estudos que avaliam o efeito do doador de óxido nítrico na regulação da germinação de sementes sob estresse salino, principalmente na germinação de espécies florestais nativas. Objetivou-se avaliar os efeitos do nitroprussiato de sódio (SNP), uma substância doadora de ON, na germinação de sementes de Senna macranthera sob estresse salino As sementes foram colocadas para germinar em diferentes potenciais osmóticos, induzidos por solução de NaCl (0,0; -0,1; -0,2; -0,3; -0,4 e -0,5 MPa). Para testar o efeito do SNP, selecionou-se os potenciais de -0,3 e -0,4 MPa, com aplicação de SNP em diferentes concentrações: 100, 200, 300 e 400 μM. Os ensaios germinativos foram conduzidos em câmara de germinação a 25oC, com fotoperíodo de 8 horas. Foram avaliados a protrusão radicular, o índice de velocidade de protrusão radicular, a porcentagem de plântulas normais, o comprimento da parte aérea e do sistema radicular, massa seca da parte aérea e do sistema radicular. O estresse salino com NaCl é prejudicial a germinação de sementes de S. macranthera. O SNP tem potencial para promover a recuperação da germinação das sementes sob estresse salino, sendo a concentração de 100 µM a mais eficaz.

Nitric oxide (NO) has been used as stimulating of the germination process for many species. However, there are few studies evaluating the effect of nitric oxide donor in the regulation of seed germination under salt stress, especially for native forest species. The objective was to evaluate the effects of SNP, an NO donor substance, on germination of Senna macranthera seeds under salt stress. The seeds were germinated at different osmotic potentials induced by NaCl solution (0.0, -0.1, -0.2, -0.3, -0.4 and -0.5 MPa). To evaluate the effect of the SNP, potentials -0.3 and -0,4 MPa were selected, applying SNP at different concentrations: 100, 200, 300 and 400 µM. Germination tests were conducted at 25 °C, with photoperiod of 8 hours. Percentage of radicle protrusion, radicle protrusion speed index, percentage of normal seedlings, shoots and roots length and dry matter were evaluated. Salt stress with NaCl is harmful to germination of S. macranthera seeds. SNP has the potential to recover germination under salt stress, especially in the concentration of 100 µM.

The activity of 1-aminocyclopropane-1-carboxylate oxidase (ACO) was characterized in seeds of the tropical legume Townsville stylo (Stylosanthes humilis) both in vitro (desalted extract of non-dormant seeds) and in vivo (entire dormant seeds). Optimum conditions for maximum in vitro ACO activity in a Trizma-HCl 100 mM buffered medium were: pH 7.0, temperature 32ºC and cofactors and co-substrate at the following concentrations: NaHCO3 30 mM, sodium ascorbate 30 mM and FeSO4 50 µM. Rates of in vitro reaction catalyzed by ACO were shown to be constant within the interval 15-150 minutes from the onset of the reaction. The apparent Km for in vitro ACO, as determined from the non-linear curve fitting to the Michaelis-Menten equation, was 156±8.3 µM ACC with a Vmax 5.4±0.08 mmol (ET) g-1 h-1 on a fresh matter (FM) basis. In vivo (control basal medium: HCl-KOH 10 mM pH 7.0, 30ºC, reaction time 15 hours) apparent Km was 230±27 µM ACC and Vmax 11.9±0.38 mmol (ET) g-1.h-1 on a FM basis. These data suggest that the enzyme exhibits a relatively low affinity for the substrate. The well-known inhibitors of ACO activity, α-aminoisobutyric acid, salicylic and acetylsalicylic acids, n-propylgallate and cobaltous ions, were highly effective in inhibiting ACO activity of Townsville stylo seeds.

A germinação de sementes dormentes escarificadas de estilosante (Stylosanthes humilis) é muito baixa em placas de Petri, mas pode ser considerável em frascos de Erlenmeyer selados devido a um acúmulo de etileno em sua atmosfera. Quando esse etileno foi adsorvido por solução de perclorato de mercúrio, a emanação do regulador gasoso das sementes dormentes e sua germinação foram drasticamente diminuídas. O etileno produzido pelas sementes dormentes, ao difundir-se na atmosfera dos frascos, promoveu maior acúmulo do próprio gás e um correspondente aumento da germinação. Sementes dormentes e não-dormentes não germinaram quando a biossíntese do regulador foi completamente bloqueada.

Germination of scarified dormant seeds of Townsville stylo (Stylosanthes humilis) is very low in Petri dishes, but may be appreciable in sealed Erlenmeyer flasks if ethylene accumulates in their atmospheres. When ethylene in the flask atmosphere was fixed by a mercuric perchlorate solution, emanation of the gaseous regulator and germination of dormant seeds were drastically decreased. On the other hand, ethylene produced by dormant seeds and accumulated in the flask atmosphere led to a further enhancement of ethylene accumulation and a corresponding increased seed germination. Germination of both dormant and non-dormant seeds did not occur when ethylene biosynthesis was completely blocked.