Seed moisture content can be used to accelerate dormancy release during after-ripening of Urochloa humidicola cv. Llanero spikelets

ABSTRACT: Increased demand for livestock products is leading to research on more productive pastures adapted to different environments. Urochloa humidicola is a species adapted to low-fertility conditions and to environments occasionally subjected to temporary flooding and with highly dormant seeds at harvest. Mechanical and sulphuric acid (H2SO4) scarification are used to release these seeds from dormancy; although, there are several side effects. Hydrogen peroxide (H2O2) is linked to dormancy release in many crop species. The objective of this research was to characterize the dormancy release and H2O2 accumulation during one year of storage in dormant spikelets of U. humidicola cv. Llanero equilibrated to 4.5% and 50% relative humidity (RH) and stored at 20 °C, during which time the seeds had moisture contents (MCs) of 0.03 and 0.1 g H2O g-1 dry weight (DW), respectively. The seeds were evaluated initially and at 3, 6 and 12 months; the seeds from spikelets or just caryopses were evaluated. Germination and dormancy percentage, H2O2 content, superoxide dismutase (SOD) and peroxidase (PRX) activity were determined. The germination and H2O2 content increased mainly in the caryopses, and SOD activity increased. Moreover, dormancy and PRX activity decreased during storage. For the first time, it was shown, in U. humidicola cv. Llanero that dormancy release during storage is caused mainly by the accumulation of reactive oxygen species (ROS) in the spikelets even under ultra-dry storage conditions (4.5% RH), and this process could be accelerated by seed storage at a MC of 0.1 g H2O g-1 DW at 20 °C.

摘要：随着畜禽产品需求持续增长，针对适配不同环境的高产牧草的相关研究日益增多。湿生臂形草（Urochloa humidicola）是一类可适应低肥力环境、偶发暂时性淹水条件，且收获时种子休眠程度极高的物种。当前常采用机械种皮划破与浓硫酸（H₂SO₄）浸种的方式打破该物种的种子休眠，但这两种手段均存在多种副作用。过氧化氢（H₂O₂）已被证实可在多种作物中促进种子休眠解除。本研究旨在探究湿生臂形草‘Llanero’品种休眠小穗在一年贮藏周期内的休眠解除与过氧化氢积累特征：将其分别平衡至4.5%与50%相对湿度（RH），于20℃条件下贮藏，此时种子的含水量（MC）分别为0.03与0.1 g H₂O·g⁻¹干重（DW）。分别于贮藏初始、第3、6及12个月时进行取样检测，检测材料包含完整小穗种子与分离出的颖果。本研究测定的指标包括发芽率、休眠率、过氧化氢含量、超氧化物歧化酶（SOD）活性与过氧化物酶（PRX）活性。结果显示，颖果的发芽率与过氧化氢含量显著提升，超氧化物歧化酶活性亦有所升高；而贮藏过程中种子休眠率与过氧化物酶活性则呈下降趋势。本研究首次在湿生臂形草‘Llanero’品种中证实：即便在超干贮藏条件（4.5% RH）下，小穗内活性氧簇（ROS）的积累仍是贮藏过程中种子休眠解除的主要诱因；而将种子含水量维持在0.1 g H₂O·g⁻¹干重、于20℃条件下贮藏，则可加速这一休眠解除进程。