7.3 plant reproduction

reproduction

• Plants can either reproduce sexually or asexually

• Succesful sexual reproduction in plants depends on: polination, fertilization, and embryo development

pollination

• transfer of pollen (usually moved by wind) from anther to stigma

  • From each pollen grain on the stigma, a tube grows down the style to the ovary

  • Once inside the ovary, the pollen tube reaches the center of the ovule where the female gamete is located

  • The male gamete is released, and fertilization occurs

Fertilization

•  happens inside the ovule in the ovary

  • Once a pollen grain has been transferred to the ovule, a diploid zygote is produced 

embryo development

• the zygote develops into an embryo, with a root and a shoot

  • It develops into a seed that will be dispersed when fully formed

flower structure

• Flowers are reproductive organs used by certain plants (angiosperms) to produce and transfer gametes between members of a species

• Most flowers posses both male and female structures (monoecious or hermaphrodite) 

male part of flower

• The male part of the flower is called the stamen and is composed of

  • Anther: producing organ of the flower , pollen is the male gamete of a flowering plant 

  • Filimant: slender stock supporting the anther , makes the anther accessible to pollinators 

female part of flower

• The female part of the flower is called the pistil or carpel and is composed of

  • Stigma: the sticky , receptive tip of the pistil, responsible for catching pollen

  • Style: the tube shaped connection between the stigma and ovule, elevates the stigma to help catch pollen 

  • Ovary: the structure that contains the female reproductive cells - ovule , after fertilization it will develop into a seed

common feautures of insect pollinated flowers

• Large brightly colored petals 

• Scent is secreted from petals to attract pollinators 

• Pollen grains: large and sticky to stick to insects

• Stigma: large and sticky to collect pollen 

• Glands called nectaries : secrete a sugar solution - attractive to many insects 

self-pollination

• Most plants are capable of self pollination (inbreeding) because they have both male and female reproductive parts

• These plants can either transfer pollen grains to the stigma of the same flower, or alternatively to a different flower of the same plant 

• Self pollination leads to inbreeding which reduces genetic diversity and increases the proportion of deleterious alleles within a population

  • Inbreeding depression: premature death, failute to thrive, infertulity among offspring

cross pollination

• Cross pollination is the transfer of pollenf rom the anther in a flower on one plant to the stigma of a flowe on another plant 

  • Promotes genetic diversity and therefore evolution 

  • Also promotes hybrid vigour: offspring of crosses between genetically unrelated plants = tend to be healthy and grow strongly

self-incompatibility

• Prevent imbreeding and increase genetic variation within a species 

• Some plants may have different male and female flowers or posses different maturation times for pollen and stigma, in order to promote cross pollination

• Other plants may have heteromorphic structures to prevent self-pollination   such as long filaments but short styles

•  Some plants may have specific genetic mechanisms - flowers produce specific proteins that are present on both the pollen and stigma → stigma will reject any pollen that posses identical proteins → preventing self-fertilization

• Plants with the same self incompatibilliy alleles cannot succesfuly polinate each other 

seed dispersal and germination

• Following fertilization, a structure called a seed will be produced

• The seed will then be dispersed and subsequently germinates to form a new plant

• Seed dispersal reduces competition between parent and offspring and helps spread

• There are different seed dispersal mechanism: wind, water, and animals

pollination vs seed dispersal

	Pollination	Seed dispersal
What is transferred?	Pollen	seeds
From where to where?	Anther to stigma	From female to a germination site
Most common methods	Wind or animals	Wind, animal, or explosion

germination

• Begins with the absorption of water to activate the seed by causing gibberellin to be produced 

• Gibberellin is a plant hormone which triggers the synthesis of enzymes capable fo digesting the food reserves within the cotyledon 

• Once the seed is metabollicly adctuvated, germination proceeds according to the following stages

  • The seed coat (testa) ruptures and the embryonic root (radicle) grows into the ground to extract key nutrients and minerals 

  • The cotyledon emerges and produces the growing shoot’s first leaf ( allowing photosynthesis to begin)

  • The growing plant continues to develop forming distinctive roots, stems, leaves, and potentially flowes