| Developing high quality legumes of saline and alkaline tolerance is a key basis to improve the low protein content of forage, in order to select forage adapted to be grown in low salinization and alkalinization habitat of Songnen region. Seed germination and seedling growth are crucial stages in the life history of a plant, which determines its subsequent growth. Experiments were conducted to study the effect of salt stress on germination and seedling growth of Medicago falcata, in comparison with two cultivars of Medicago sativa (cw400 and GN 2). Seeds were germinated under conditions of 0,20,40,60,80,100,120,140,160,180,200 mmol/L NaCl, seed germination percentage and germination index, seedling growth, as well as proline and Na+, K+ contents of three materials were measured. The results showed germination percentage and index of all three materials were suppressed to different extent as salt concentration increased, and the suppression was more obvious in higher salt solution. In comparison with two cultivars of cw400 and GN2, M. falcata showed significantly lower in germination percentage and index, but the growth of radicle was not affected by salt solution and there were no significant differences between various treatments and control. The recovery test showed that seeds of three materials could keep viability in salt solutions. The total germination of M. falcata and cw400 reached 100% in 60mmol/L NaCl, but only the total germination of M. falcata reached above 90% in all solutions with the highest recovery percentage and there were no significant differences between treatments. As an osmotic regulator, proline could quickly accumulate in M. falcata seedling. For M. falcata, Medicago sativa cw400 and GN2, the content of proline in 100 mmol/L were 3.1, 2.3 and 1.4 times respectively of that in control. The ratio of Na/K increased with concentration of NaCl solution. The ratios of Na/K of M. falcata, cw400 and GN2 were31.4 46.6 and 44.1 times respectively of that in control. In conclusion, the salt tolerance of M. falcata was stronger than Medicago sativa, and M. falcata was more applicable for growth in Songnen grassland. As a nutrient storage organ, cotyledon provides reserves during seed germination. After emergence, cotyledon photosynthesizes immediately and functions as a"source"together with the true leaves during seedling development. The characteristics of cotyledons per se determine the particularity of its growth, five species Suaeda glauca, Kochia sieversiana, Amaranthus retroflexus, Protulaca oleracea and Xanthium strumarium were used to study the differences of growth patterns between cotyledons and true leaves, and the extent of seedling normal growth dependence to cotyledons and true leaves. The experiments were conducted between June and August in 2006. The length and width of cotyledon and the first true leaf were measured over time. The two cotyledons were removed at different time to study the dependence of seedling on cotyledon and different numbers of leaves were removed to study the dependence of seedling normal growth on true leaves.The main results showed that the growth of cotyledon accorded with exponential growth mode y= a·(1-e-bx), cotyledons spread out after emergence, grew quickly to the maximum leaf area and entered plateau. The first true leaf growth accorded with logistic growth mode y = a/[1+e-(x-x0)/b], the process followed"slow-fast-slow"basic law, as grew slowly at the beginning and gradually quickened afterward, then slowed down again to cease eventually.The dependence of seedling growth to the photosynthesis of cotyledons was stronger as the seed was smaller. Cotyledon removal significantly inhibited seedling growth, the inhibition was more obvious as removed earlier. As the removal time postponed, the inhibition became smaller and smaller until disappeared. The growth of S. lauca, K. ieversiana, A. retroflexus, P. oleracea and X. strumarium seedlings disengaged from the dependence on cotyledon on the day15, 15, 13, 14, 9respectively. The photosynthates from cotyledons mostly transported to the above ground part of the seedling in the early stage. As abundance of true leaves photosynthesis, the photosynthates gradually transfered to underground and provided for roots.During the early stage of seedling growth, the contribution of cotyledon is more important than that of true leaves. In this experiment, the contribution of one cotyledon is equal to that of the first pair of true leaves for A. retroflexus, P. oleracea and X. strumarium. As true leaves grew, the function of cotyledons gradually weakened. Since the second pair of true leaves appeared, the source of seedling photosynthates was mainly the true leaves. The contribution proportion of one cotyledon decreased, when the true leaves played a major role. For P. oleracea, lack of one true leaf of the pair can be compensated by the other, but for P. oleracea and X. strumarium, the photosynthesis contribution of two true leaves of each pair could not be compensated by each other. The true leaves of S. lauca and K. ieversiana did not grow in pair, many true leaves appeared simultaneously, and quickly played a major role in photosynthesis, thus lack of minor true leaves had no significant effects on seedling growth. |
PDF Full Text Request