Effect of exogenous ABA on adzuki bean yield under chilling stress
15°C during flowering stage can significantly affect the yield of adzuki beans. For LXD 4, the yield shows CK>T2 at each time and the result of significant analysis showed that CK was higher than T2 from 2d to 5d. In addition, with the extension of the treatment time, the greater the degree of yield loss, T2 of LXD 4, compare with 1d, the yield at 5d decreased by 10.30 g per pot, a decrease of 59.81%. For TJH, the yield shows that, CK was consistently higher than T2, significantly. Under low temperature conditions, spraying exogenous ABA can inhibit production reduction. For LXD 4, T1 was significantly higher than T2 by 6.72%, 7.69%, 10.85%, 9.92% and 17.77% during treatment from 1d to 5d. For TJH, T1 was significantly higher than T2 by 6.41%, 15.67%, 20.47% and 37.04% from 2d to 5d (Table 2).
As shown in Table 3, it is clear that chilling stress increased the hundred-grain weight. For LXD 4, T2 was significantly heavier than CK by 3.23%, 8.00%, 16.30%, 8.06% and 4.30% during treatment from 1d to 5d. For TJH, T2 was significantly heavier than CK by 19.24%, 10.82%, 12.04%, 16.71% and 10.88% during treatment from 1d to 5d. Spraying exogenous ABA reduced the hundred-grain weight of adzuki bean. For LXD 4, T1 was lighter than T2 by 0.73%, 0.83%, 1.38%, 1.97% and 1.24% during treatment from 1 to 5 days. For TJH, T1 was higher than T2 by 3.44%, 1.64%, 1.35%, 5.48% and 2.15% during treatment from 1 to 5 days.
Effect of exogenous ABA on MDA content in adzuki beans leaves under chilling stress
As shown in Fig 2, the MDA content showed an increasing trend after low temperature treatment during the flowering stage. Compared with CK, T2 of LXD 4 significantly increased by 19.68 nmol·g-1, 25.45 nmol·g
-1, 30.00 nmol·g
-1, 39.89 nmol·g-1 and 40.03 nmol·g
-1. T2 treatment of TJH significantly increased by 14.17 nmol·g
-1, 24.42 nmol·g
-1, 30.48 nmol·g
-1, 39.79 nmol·g
-1 and 43.91 nmol·g
-1. Exogenous ABA can significantly inhibit the increase of MDA content under low temperature conditions. The analysis of variance showed that after treatment for 1 to 5 days, both LXD 4 and TJH showed that T1 was significantly lower than T2.
Effect of exogenous ABA on photosynthesis in adzuki beans leaves under chilling stress
It can be seen from Fig 3 that, with the extension of the stress time, compared with CK,
Pn,
Gs,
Ci and
Tr in T2 treatment reduced significantly both of LXD 4 and TJH. At the same time, under natural environment, spraying exogenous ABA has the effect of increasing
Pn,
Gs,
Ci and
Tr, especially
Pn,
Gs and
Tr can be significantly increased (Fig 3A, 3B, 3C and 3D).
Under low temperature conditions, spraying with exogenous ABA can improve the photosynthesis. As shown in Fig 4A, compared with T2, T1 treatment of LXD 4 increased by 4.84%, 14.02%, 12.01%, 21.31% and 18.39% and the ANOVA results showed that there was a significant difference at the 4th and 5th day. TJH showed that, T1 was significantly higher than T2 by 14.43%, 9.19%, 21.18%, 10.93% and 16.39%.
With the
Gs, it can be seen from Fig 3B, compared with T2, T1 treatment of LXD 4 significantly increased by 45.84%, 19.46%, 57.66% and 20.56% from 2d to 5d. TJH showed that T1 was significantly higher than T2 by 17.39%, 4.11% and 42.23% from 3d to 5d.
As shown in Fig 3C, compared with T2, T1 of LXD 4 increased by 5.67%, 8.30%, 9.77%, 19.54% and 13.95%, the analysis of variance showed that T1 was significantly higher than T2 at each time. For TJH, T1 was significantly higher than T2 by 6.90%, 10.58% and 11.47% during treatment from 3 to 5 days.
t can be seen from Fig 3D that, spraying exogenous ABA can inhibit the reduce of
Tr, compared with T2, T1 of LXD 4 was significantly higher than T2 by 19.54%, 20.33%, 28.17% and 140.35% from 1 to 4 days. For TJH, T1 was significantly higher than T2 by 47.05%, 72.28% and 20.91% from 3 to 5 days.
Effect of exogenous ABA on the content of osmotic regulation substances in adzuki beans leaves under chilling stress
Under the normal temperature condition, soluble sugar, soluble protein and proline content in adzuki bean leaves showed a stable change trend, but the content of these substances in leaves had an upward trend with the increase of chilling time intensity. As shown in Fig 4, the soluble sugar, soluble protein and proline contents in T2 were always significantly higher than CK.
Under low temperature condition, spraying with exogenous ABA can further increase the content of osmotic regulation substances. As shown in Fig 4A, compared with T2, T1 treatment of LXD 4 significantly increased than T2 by 1.07% and 8.93% at 1d and 2d. TJH showed that, T1 was significantly higher than T2 at each time. With the soluble protein, it can be seen from Fig 4B that, compared with T2, T1 treatment of LXD 4 increased by 1.74%, 6.00%, 10.12%, 16.71% and 17.40%, the analysis of variance showed that after treatment 3 to 5 days, it showed that T1 was significantly higher than T2. TJH showed that, when treated from 4 to 5 days, T1 was significantly higher than T2 by 2.53% and 4.05%. The increasing effect of exogenous ABA on proline is very obvious. As shown in Fig 4C, compared with T2, T1 was always significantly higher than T2 both of LXD4 and TJH.
Photosynthesis is a determinant of crop productivity and an important indicator of crop response to environmental stress. Photosynthesis is most sensitive to chilling stress
(Allen et al., 2001) and chilling stress significantly inhibits
Pn, resulting in a decrease in yield
(Strauss et al., 2007). This study also found that low temperature led to a significant decrease in
Pn and at the same time,
Gs,
Ci and
Tr were also significantly reduced. We believe that this is because low temperature causes ROS metabolism disorder, which affects the structure and activity of photosynthetic organs, which in turn affects the capture, transformation and distribution of light energy in leaves. This view is also consistent with
(Ayub et al., 2011).
When encountering adversity stress, plants will automatically turn on the protection system to resist the threat of adversity factors and then try to maintain normal physiological and metabolic activities and avoid damage
(Xiang et al., 2019b). Plants subjected to low temperature stress will turn on a series of stress self-protection mechanisms and these protection systems coordinate organically with each other to minimize damage
(Xiang et al., 2019a). Exogenous ABA has the function of regulating the stress resistance physiology of plants and has multiple pathways in resisting low temperature stress. The main stress response is to increase the content of osmotic regulators to regulate the content of MDA decreased. This study found that, exogenous ABA can effectively change the physiological indicators of stress resistance in adzuki bean under low temperature conditions. The application of exogenous ABA can significantly increase the content of osmotic adjustment substances, further reduce the content of MDA (Fig 2).
We can also see from the results of this study that spraying of exogenous ABA can significantly increase the yield per pot of adzuki bean (Table 2) after low temperature stress and effectively alleviate the impact of low temperature on yield.