PlantDevelopment on emsenn.net

Double Fertilization

Thu, 02 Apr 2026 00:00:00 +0000

Double fertilization: the defining reproductive innovation of angiosperms, in which a single pollen tube delivers two sperm cells to the ovule. One sperm fuses with the egg cell to form the diploid zygote that will develop into the embryo; the other fuses with the central cell’s two polar nuclei to form the triploid endosperm. This two-for-one event is unique to flowering plants and ensures that endosperm is produced only when fertilization occurs, eliminating wasted provisioning of unfertilized ovules.

Gibberellin

Thu, 02 Apr 2026 00:00:00 +0000

Gibberellin: a class of plant growth-promoting hormones that stimulate stem elongation, break seed dormancy, promote flowering, and regulate fruit development. Over 130 distinct gibberellin structures have been identified (GA₁, GA₃, GA₄ being among the most bioactive), but all share a common four-ring gibban skeleton. The hormone was first discovered through study of the “bakanae” (foolish seedling) disease of rice, caused by the fungus Gibberella fujikuroi, which secretes gibberellins causing extreme stem elongation.

Ovule

Thu, 02 Apr 2026 00:00:00 +0000

Ovule: the structure within a flower’s ovary that contains the female gametophyte (embryo sac) and develops into the seed after fertilization. The ovule is the female counterpart to the pollen grain, enclosing the egg cell, supporting tissues, and protective layers. Its development is simultaneous with pollen maturation in the anther, but ovule development is typically much slower and often stops at a specific stage until fertilization triggers resumption.

Structure

A mature ovule consists of several layers and regions:

Pollen

Thu, 02 Apr 2026 00:00:00 +0000

Pollen: the male gametophyte of seed plants, produced within the anthers of the stamen. Each pollen grain is a compact cellular package containing the male gametes (sperm cells) and the tissues necessary to deliver them to the ovule. Pollen is the most abundant organism in the global biosphere by cell count and is fossilized with extraordinary resistance to degradation — pollen grains recovered from sediments millions of years old remain identifiable to species, making palynology (the study of pollen) a cornerstone of paleobotany and paleoclimatology.

Senescence

Thu, 02 Apr 2026 00:00:00 +0000

Senescence: the programmed developmental process by which plant organs (characteristically leaves, but also flowers, fruits, and entire annual plants) undergo controlled degradation, yellowing, and eventual death. Senescence is not passive decay or disease — it is an active, genetically regulated process that coordinates the dismantling of cellular structures with the reclamation of valuable nutrients (nitrogen, phosphorus, minerals) for reallocation to other parts of the plant.

Senescence is initiated by environmental cues: photoperiod (shortening day length in autumn) is the primary trigger in temperate plants, signaling that winter is approaching and photosynthesis will soon be impossible; cold stress can accelerate senescence; drought induces premature senescence by reducing water availability for expansion and photosynthesis; pathogen attack triggers localized senescence in affected tissues. Senescence is also hormonally regulated: ethylene (the ripening and senescence hormone) promotes leaf senescence; cytokinins delay senescence, maintaining photosynthetic capacity and nutrient retention; abscisic acid (ABA), released under stress, accelerates senescence as an adaptation to drought or cold.