**Plant Growth and Development**:
– A vascular plant begins from a single-celled zygote formed by fertilization.
– Plant embryo forms through embryogenesis with roots and shoots developing.
– Organogenesis leads to the growth of leaves, stems, and roots.
– Primary growth lengthens roots or shoots, while secondary growth widens them.
– Directional growth occurs in response to stimuli like light, gravity, water, and physical contact.
– Morphological variation in form and structure within individual parts.
– Variation in leaves and other organs due to positional effects, environmental effects, and juvenility.
– Temperature affects plant structures and maturation processes.
– Juvenility results in differences between young and adult plant organs.
– Transition from early to late growth forms is known as vegetative phase change.
– Plant growth and development are regulated by specific hormones and growth regulators.
– Endogenous hormone levels are influenced by plant age, environmental conditions, and external sources of growth regulators.
– Understanding plant hormones and growth regulators is essential in agricultural practices.
**Adventitious Structures and Root Development**:
– Adventitious roots, buds, and shoots develop in unusual locations.
– Adventitious roots form in parenchyma or phloem parenchyma in stems.
– Adventitious buds develop on roots, leaves, or shoots in response to stimuli.
– Adventitious buds help in replacing lost branches and can develop on mature tree trunks.
– Adventitious rooting can be a stress-avoidance acclimation.
– Commercial propagation utilizes plant stems’ ability to form adventitious roots.
– Plant hormones like auxins are applied to promote adventitious root formation.
– Modified forms of roots such as tuberous roots, fasciculated roots, nodulose roots, stilt roots, and prop roots provide various functions in plants.
**Plant Development Stages and Processes**:
– Plant development involves stages like embryogenesis, organogenesis, and growth.
– Cell elongation contributes to plant growth by increasing cell length.
– Growth processes are influenced by environmental factors and plant hormones.
– Differentiation of plant tissues and organs is crucial for proper growth.
– Understanding plant development stages helps in optimizing growth conditions.
– Some leaves develop adventitious buds for vegetative reproduction.
– Coppicing promotes rapid growth of adventitious shoots for various purposes.
**Leaf and Flower Development**:
– Genetics play a significant role in leaf shape development.
– Leaf primordium initiation involves suppression of specific genes.
– Gibberellin levels increase to initiate leaf growth.
– Various genetic factors are involved in leaf primordia development.
– Flower development in angiosperms involves gene expression in meristems.
– The ABC model describes the biological basis of flower development.
– External stimulus triggers meristem differentiation into a flower meristem.
– Interactions of gene products determine organ identity in floral verticils.
**Rose Scent Evolution**:
– ODO1 regulates benzenoid biosynthesis.
– OOMT1 and OOMT2 contribute to major scent compound biosynthesis.
– DMT is produced by many rose varieties.
– Some rose varieties do not emit DMT due to lack of OOMT genes.
– OOMT protein is tightly associated with petal epidermis membranes.
– Certain compounds in floral scent appeal to specific pollinators.
– In Petunia hybrida, volatile benzenoids are produced for floral smell.
– Regulation of enzymes in the benzenoid biosynthetic pathway is not fully understood.
Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born (or hatches from its egg), it has all its body parts and from that point will only grow larger and more mature. However, both plants and animals pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.
According to plant physiologist A. Carl Leopold, the properties of organization seen in a plant are emergent properties which are more than the sum of the individual parts. "The assembly of these tissues and functions into an integrated multicellular organism yields not only the characteristics of the separate parts and processes but also quite a new set of characteristics which would not have been predictable on the basis of examination of the separate parts."