Seed respiration of sorghum [<I>Sorghum bicolor</I> (L.) Moench] during germination as affected by temperature and osmoconditioning

Abstract

Seed respiration has been utilized as an index of seed vigour and has correlated well with seedling development. We examined the respiration process as affected by temperature and osmopriming during imbibition in two cultivars of sorghum [Sorghum bicolor (L.) Moench] differing in capacity to germinate at low temperatures. Respiration of imbibing seeds was measured with a specially built apparatus linked to an infrared gas analyser. Seed respiration at the beginning of the imbibition process strictly depended on temperature (T). T also greatly affected the total CO2 respired to reach the first germination event, which significantly increased as T declined from the optimum. Osmopriming affected seed respiration differently in the two cultivars. In the cold-tolerant cultivar (Brandes), osmopriming reduced the total thermal requirements and, at T close to the minimum for germination, the energy required to achieve the first radicle protrusion. In the cold-sensitive cultivar (H128), osmopriming lowered base T for respiration and reduced the requirements for total CO2 respired, allowing germination even at 10°C. The cold-tolerant cultivar always maintained higher respiration rates than the cold-sensitive one, showing a greater capability of mobilizing energy from reserves. Germination time (i.e. GR50) related well to cumulative seed respiration down to a threshold value of cumulative CO2, after which GR50 was more affected by T than was cumulative respiration. Seed water uptake significantly slowed with decreasing T, and was accelerated by osmopriming. However, water imbibition rate influenced the start of seed respiration, but not the subsequent rate of metabolic activity preceding germination. Seed respiration was a good indicator of the activation of germinative metabolic processes, although under extreme T conditions the seed populations still respired, even if at low levels, but did not germinate rapidly or completely.

Alterações fisiológicas e bioquímicas em sementes de arroz submetidas ao estresse térmico

“…Isto indica que houve modificações na ação das enzimas A maior atividade enzimática evidenciada a partir de 25 ºC não favoreceu o crescimento inicial das plântulas, pois a partir dessa temperatura o crescimento e massa seca de parte aérea e raiz diminuíram (Figura 2). Provavelmente houve transformações degenerativas que levaram ao rápido consumo das reservas das sementes logo no início do processo de germinação (PATANÉ et al, 2006), o que pode ter diminuído a eficiência respiratória, conduzindo ao menor aproveitamento nos processos de síntese, provocando decréscimo da germinação e do vigor das sementes, com reflexos direto em suas plântulas. Na menor temperatura (15 ºC) a respiração aconteceu de forma mais lenta e as reservas, por sua vez, não foram utilizadas de forma rápida, o que pode ter favorecido seu desdobramento e, a sua consequente utilização pelas plântulas.…”

“…Alguns trabalhos estão sendo desenvolvidos no sentido de avaliar essas mudanças nas atividades de enzimas que ocorrem nas sementes e plântulas estressadas. Normalmente, nesses trabalhos são utilizadas enzimas importantes no processo de respiração celular, como por exemplo, a enzima malato desidrogenase (COUTINHO et al, 2007;PATANÉ et al, 2006;SANTOS et al, 2005).…”

Effect of temperature on passion fruit emergence and seedling vigor

“…Upon subjected the seedlings to the highest temperature (25-35 °C), a reduction in seedling dry matter of 21.80% was observed, even though a statistical difference between the ranges 20-30 °C and 25-35 °C was not observed. Temperatures considerably higher than the optimum temperature for seedling growth and development contribute to degenerative transformations that bring about rapid consumption of seed reserves, which may affect respiration efficiency, leading to lower utilization in synthesis processes, with direct reflection on biomass accumulation in the seedlings (Patané et al, 2006;Marini et al, 2012).…”

Antioxidant activity of corn seeds after thermal stress

“…Extreme temperatures can induce degenerative changes that spurred the initial growth of seedlings leading to the rapid consumption of seed reserves, during the early germination process (PATANÉ et al, 2006). There was a strong investment in the initial growth of seedlings in order to not impair the processes of synthesis and release of energy, as a way to continue the autotrophic germination process, characterizing a defense strategy of the seeds subjected to such temperatures.…”