9.2: Sensory Systems - Plants

chromophore

A molecule that can absorb light, causing a change in energy state, playing a crucial role in photosynthesis and plant signaling.

photoreceptors and chromophore

photoreceptors mediate plant’s responses to light due to containing a protein component bound to chromophore. Each chromophore om specific receptors absorbs certain wavelengths causing structural changes in receptor = signalling cascade. Can lead to gene expression affecting growth and morphology

phytochrome photoreceptors

detects red and far-red light. Have 2 distinct interconvertible forms = inactive Pr and active Pfr

affect of shade on plant growth

phytochrome photoreceptors detect shade by sensing the ratio of red to far-red light. Pr absorbs red light then converts to active Pfr triggering responses. In shade far-red light is higher converting Pfr to Pr = signals to elongate stem and adjust growth to reach light

biological clocks

internal timekeeping mechanisms in plants that regulate various physiological processes, including flowering and growth based on environmental cues such as light and temperature. follows circadian rhythm and responds to photoperiodism

circadian rhythm

24 hour internal clock that regulates behaviour and physiology, influenced by light and other cues

role of phytochrome in detecting seasons

Plants measure day length using phytochromes to regulate photoperiodism. During the day, Pr absorbs red light and converts to Pfr. At night, Pfr declines slowly back to Pr or is broken down. The Pr/Pfr ratio at dawn lets plants sense day length and trigger seasonal responses.

phytochrome during winter

Long nights. Pfr levels may drop completely by sunrise due to prolonged darkness, signaling the plant to enter a dormant state.

phytochrome in summer

shorter nights. Considerable amount of Pfr remains at sunrise, promoting growth and flowering in response to longer daylight hours.

photoperiodism

plant’s response to day and night length, influencing their growth, flowering, and dormancy.

gravitropism

the directional growth of plants in response to gravity, affecting root and shoot orientation.

• positive = downward growth of roots

• negative = upward growth of shoots

statoliths

are amyloplasts specialized for gravity sensing in root cap of plants. They settle downward in response to gravity = asymmetrical elongation of root tip

• upper side of root = growth stimulated, lower side = suppressed - roots curve as grows down

thigmotropism

directional growth by plants in response to touch.

• negative = roots grow away

• positive = tendrils of climbing plants grow towards. Touch causes contraction of cells on contact-side and elongation non-contact side = tendrils wrap around object securing plant

Consider and describe how the P_r:P_fr ratio differs between plants at low latitudes (e.g. 0°) compared to those at high latitudes, given how day length changes the ratio

low latitude = fairly constant Pr:Pfr ratio year-round

high = plants experience large seasonal changes in Pr:Pfr