Iranian Journal of Seed Research

Extended Abstract
Introduction: Soybean (Glycine max (L.) Merrill) is the primary source of vegetable oil. Even in desirable conditions, soybean seeds lose their viability in long term storage. Many factors contribute to seed deterioration, including genetic factors, mechanical damage, relative humidity, storage temperature, seed moisture content, existence of microflora, and seed maturity, which reduce seed quality and make seeds unfit for cultivation purposes.
Materials and Methods: In order to investigate the effects of seed deterioration on seed germination and also the effects of salicylic acid and ethylene on the improvement of deteriorated seeds of G. max., accelerated aging test for 0, 6 and 10 days and natural aging test for 6 months were conducted. After aging conditions, seeds were imbibed with 50 µM salicylic acid and 10 µM ACC (precursor of ethylene) for 6 hours at 25 °C. In addition, after natural and accelerated aging tests, a bunch of seeds was used without any hormonal treatment (i.e., dry seeds) as control seeds. The seeds’ germination percentage, total sugar, fructose, and glucose were investigated. Moreover, the gene expression of GAI1 and LOX1 was measured on dry seeds and under imbibition of water, salicylic acid and ACC at 6, 12 hours using Q-RT-PCR method.
Results: The germination results showed that increasing number of aging days led to a decrease in germination. Total sugar content in seeds aged for 6 days did not have a significant difference, as compared with non-aged seeds. However, total sugar content in seeds aged for 10 days was significantly higher than non-aged seeds. Increasing accelerated aging levels from 0 days to 10 days led to increases in glucose and fructose contents in dry seeds. In addition, genes exhibited different expressions in different days and hours. Increasing aging from 0 days to 10 days led to increases in GAI1 gene expression. Moreover, LOX2 expression increased in accelerated aging from 0 to 6 days. LOX2 gene expression in naturally dried aged seeds also increased and was higher than that in non-aged seeds. SA and ACC had different effects on measured values.
Conclusion: In general, it can be concluded that the deterioration of seed quality and vigor result from numerous degradation processes and disruption in seeds’ physiological activity. This study showed that aging is associated with an increase in total sugar, glucose and fructose levels. In addition, the expression of the genes involved in the germination is also affected. Increases in LOX2 gene expression were observed in both accelerated aging and natural aging pathways. GAI1 gene expression increased in accelerated aging. However, in normal aging, it decreased.
 

Highlights:

1. Identifying the role of LOX2 and GAL1 genes in soybean seed deterioration.
2. Investigating seeds’ physiological responses under natural and laboratory aging conditions.

Extended abstract
Introduction: The effects of temperature increases on the growth of tomato fields are among the obvious results of global warming and are considered an important issue that should be investigated. To maintain and develop the cultivation systems of this crop, a proper understanding of the heat tolerance mechanisms and physiological responses in tomatoes should be achieved. The primary objective of this research is to discover the impact of heat stress on the germination and growth of pollen grains in research tomato germplasms. The researchers' knowledge about the response of different tomato cultivars to abiotic stresses is limited and only the effects of enzymes involved in the response process, heat shock proteins and some hormones have been investigated. The process of detecting heat stress-sensitive stages and their enhancement is facilitated by having a correct understanding of physiological processes.
Materials and methods: The seeds of heat-resistant (LA2661 and LA2662) and -sensitive (LA3911) research cultivars of tomato were used to evaluate the effects of increasing day and night temperatures. The obtained seedlings were grown under optimal temperature conditions (24^°C day/18^°C night), and after observing the first flower primordium, were incubated in growth chambers to apply daytime heat stress treatments, including temperatures of 28^°C, 32^°C and 36^°C day/18^°C night and night stress treatments including temperatures of 28^°C, 32^°C, and 36^°C at night/ 24^°C day for 7 days. Pollen grains were then evaluated for their survival, germination, and growth.
Results: The findings of the daytime heat stress tests show that the percentage of survival and germination of pollen grains and growth of pollen tubes of cultivars LA2661, LA2662 and LA3911 decreased as daytime temperature rose from 24­^°C to 36­^°C. This reduction is more noticeable for the sensitive cultivar LA3911. Degraded pollen grains increased in the LA3911 cultivar due to heat stress. The survival percentage of pollen grains in all three studied cultivars decreased due to the application of heat stress at night. The resistant cultivars LA2661 and LA2662 had a higher germination percentage compared to the sensitive cultivar LA3911. Pollen grains germination decreased by 50% as a result of increasing the night temperature from 18^°C to 36^°C. Pollen tube length was reduced in both cultivars and night treatments.
Conclusion: The effects of heat stress in the early stages of flowering when flowers are visible are high, and reproductive stages are very sensitive to high temperatures and affect fertility and processes after insemination, and finally, they lead to yield loss. The daytime temperature increase relative to the natural temperature range (22^°C to 24^°C) during growth severely impacts the number of pollen grains released from tomato flowers. The number of non-living pollen grains is higher at 36^°C day and 32^°C and 36^°C night temperatures compared to optimal temperature conditions. It appears that the increase in nighttime temperature results in more severe consequences than the increase in daytime temperature.

Highlights:

1. Night heat stress was assessed as a factor that influences the germination and survival of tomato pollen grains.
2. Image analysis was used to measure the length of the pollen tube.
3. The effect of thermal stress on pollination was investigated during a specific period of reproductive growth.