Investigating changes in gibberellin and abscisic acid in the leaves and twigs of different age groups Kochia prostrata (L) schrad and its effect on germination and seed dormancy characteristics under prechilling treatment

Few studies have been conducted on the age of mother plants and their effects on seed germination traits. Maternal plants of different ages owing to morphological and phytochemical differences, have different effects on phytochemical and seed germination traits. The aim of this study was to investigate the morphological and phytochemical differences of different ages of Kochia prostrata maternal shrubs and their effects on the characteristics of their seed germination traits. Investigating the depth of seed dormancy at different ages and the impacts of prechilling on breaking seed dormancy have been other goals of this study.

In the study population, five plants from each age group were randomly selected and morphological traits were measured and then, were cut from the collar section and their age was determined in the laboratory. The maternal plants were divided into three categories: young, mature, and old. During the seed collecting season, 10 plants from each age group were randomly selected based on collar diameter and canopy cover; furthermore, in order to determine the average seed production per plant and 1000-seed weight, their total seeds were collected separately in zippered plastic bags. The leaves and twigs were sampled by the age of maternal shrubs. Seed germination experiments were performed as a completely randomized factorial design in 3 replications. The first factor was the seeds of different age groups (young, mature and old) and the second factor was the prechilling in -2 degrees Celsius. Phytochemical and germination traits of treated and untreated seeds including starch, total sugar, alpha-amylase enzyme activity, germination percentage, germination rate, percentage of normal seedlings, root length, stem length, seed vigor and amount of gibberellin and abscisic acid hormones were measured. The amount of gibberellin and abscisic acid in plant organs (leaves and twigs) was also measured by age groups of maternal shrubs.

The results showed that the mature shrubs, with the appropriate height and canopy cover, had the maximum seed production per plant (13.02 g) and had a significant difference with other groups (P <0.01). Also, the 1000-seed weight of this age group (2.11 g) had a significant difference with young shrubs (P <0.01). Mature shrubs had the highest amount of free gibberellin hormone (15.82 mg / l) and the highest amount of abscisic acid (10.82 mg / l) marked a significant difference (P <0.01). Higher levels of abscisic acid in the mature plants indicate greater compatibility with arid and semi-arid environments. Seeds of mature plants with 0.726 mg / l gibberellin showed a significant difference with seeds of young shrubs (1.97 mg / l) (P <0.01), but the amount of internal abscisic acid in the seeds did not differ significantly. The ratio of gibberellin to abscisic acid in seeds of mature shrubs (0.383) was not statistically different from the ratio in seeds of young shrubs (0.726) (P <0.01), but was lower, indicating deeper dormancy in the seeds of the mature age group. Prechilling treatment had the greatest effect on the seeds of mature plants, so the amount of free and bond gibberellin increased to 12.01 and 8.99 mg / l, respectively, and the ratio of gibberellin to abscisic acid increased to 9.41. This has led to broken seed dormancy, increased activity of alpha-amylase enzyme and decomposition of starch into simple carbohydrates, increased percentage of normal seedlings, increased root length and seed vigor, which is most noticeable in seeds of mature plants.

Different age groups of K.prostrata differ in phytochemical and morphological characteristics which affect the germination and phytochemical characteristics of their seeds and controls and regulates the mechanism of dormancy in seeds.