Measurement of Some Chemicals in Rice and Effect of Exogenous Substances Under the Salinity Stress at Flowering Stage

Abstract

Salinity is one of the most challenging problems that adversely affects growth and development of rice. The objectives of this study are to investigate salinity stress and the effects of foliar application of proline and trehalose at flowering stage on morphological, biochemical features and proline synthesis gene in rice. The two experiments were conducted separately using different types of exogenous substances: proline and trehalose, from January to May 2020. The experiment design used 3x4x4 factorial in Completely Randomized Design (CRD) with three replications. Three types of rice varieties (factor A) including Chai Nat 1 (CNT 1), Pathum Thani 1 (PT 1) and a salt-tolerance variety from Indonesia, Inpari 35 (IN 35) were planted in 4 salinity levels (factor B) including 0, 5, 10 and 15 dS/m with 4 different levels of proline or trehalose application (factor C) including 0, 50, 100 and 150 mM. In biochemical measurement revealed that after the proline and trehalose spray, the accumulation of proline in leaf and stem, starch content both under no salinity and salinity conditions mainly depended on genetics. As for accumulation of these chemical compositions: the sugar content, proline content or starch, the increase or decrease in the leaf or the stem depends on many factors including the type of substance used (relation of the sprayed substance and the characteristics what to be measured), the change in the amount of those substances after salinity exposure (that reflects the salinity tolerance of various varieties). However, under salinity conditions (5-15 dS/m salinity), the use of external substances such as proline or trehalose in all concentrations can promote by increasing many characteristics; excluded the water content. In reproductive stage may be one stage that is tolerant of leaf dehydration when plants growing in saline soil. Nevertheless, under no salinity condition (0 dS/m), the effect of exogenous proline or trehalose was found mostly in agronomic characteristics, yield components, and yield, but rarely affected in chemical contents (proline, sugar, starch) that accumulated in plants. Assessed by the synthesis of complementary deoxyribonucleotide (cDNA), at 10 dS/m salinity, CNT 1 and PT 1 are partially able to synthesize proline automatically in leaves, although was no received external proline sprays. Nevertheless, when proline at 50-100 mM is sprayed externally, there has been an increase in the stimulation of proline synthesis in the plant. However, may have the limit of the quantity of exogenous proline be used to stimulate the synthesis of this substance inside plants. The external proline that plant was received by spraying did not increase the accumulation in the plant at 150 mM proline. For IN 35, did not respond to increase leaf proline synthesis, although has been stimulating by proline spraying. The highest salinity level (15 dS/m), exogenous proline use does not encourage the increased synthesis of this substance in the leaves in all rice varieties. Therefore, increased deposition of proline in leaves may be obtained directly from spraying.

For the chlorophyll contents, the use of proline was higher in effectiveness to increase the values more than trehalose. The results showed that Thai rice varieties after proline spraying at high salinity (at 15 dS/m salinity) showed an increase in the accumulation of proline and sugar, although not very high, but more than in IN 35. IN 35 is resistant to salinity and to accumulate the proline in plant cells of leaves autonomic. For starch content, effect of trehalose applying showed very little change compared with proline spraying both in leaves and stems in each variety. Considering the damage on characteristics affected by salinity, the varieties have less effect or high tolerance ability to salinity is IN 35, and lower in two Thai varieties. Among Thai rice varieties, CNT 1 was affected by salinity in lower magnitude in most of the characteristics and was more sensitive by applying both proline and trehalose more than PT 1. For these reasons, CNT 1 seems higher tolerance ability to salinity more than PT 1. Since at 5 dS/m salinity, plant height and yield components were received the negative effects. Proline and trehalose showed no effect or little effect (with no significant difference) in plant height, the number of fertile tillers, and 1,000-seeds weight because these characteristics were established not consistent with the time for substance use. However, these external substances can increase the value in panicle length and filled grain percentage. Further, the effect on the percent of grain filling is likely to be consistent with the effect on pollen viability. For grain yield, to increase by applying both substances: proline and trehalose, at the flowering stage, especially at salinity conditions.

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