BIOL1030 Chap.10 Plant Signals, Timing and Stress Responses
Plant Signals, Timing and Stress Responses
Plant Signals, Timing and Stress Responses combines Lectures 8 and 9, which ask how plants coordinate growth without a nervous system and how they survive changing environments.
It traces the route from receptor to signal transduction, gene expression and development, defines plant hormones, and shows auxin at work in phototropism, gravitropism, apical dominance and lateral root formation, alongside cytokinin, strigolactone, gibberellins, abscisic acid and sugars as signals.
The second half turns to light and time: phototropins, cryptochromes and phytochrome, shade avoidance, circadian clocks and photoperiodism based on night length. It ends with systemic signalling, stress and yield gaps, priming, acclimation, adaptation and Grime's competitor, stress-tolerator and ruderal strategies.
What this chapter covers
- 01
Signal perception, transduction and gene expression
- 02
Auxin transport, acid growth and tropisms
- 03
Branching networks: auxin, strigolactone and cytokinin
- 04
Sugars as signals and biomass allocation
- 05
Photoreceptors, phytochrome and shade avoidance
- 06
Circadian clocks and photoperiodism by night length
- 07
Priming, acclimation, adaptation and Grime's strategies
Worked example · free
Predict flowering from night length
- 1The critical variable is the longest uninterrupted night compared with the critical length, not the day length.
- 1(a) A 14-hour night exceeds 10 hours, so the short-day plant flowers and the long-day plant does not.
- 1(b) An 8-hour night is shorter than 10 hours, so the long-day plant flowers and the short-day plant does not.
- 1(c) The red flash converts Pr to Pfr and splits the night into two 7-hour periods, so the plants respond as to a short night: the long-day plant flowers.
Key terms
- Apical dominance
- Suppression of lateral buds by the shoot apex, carried by auxin.
- Phytochrome
- A red and far-red light receptor that switches between Pr and Pfr and regulates germination, shade avoidance and flowering.
- Photoperiodism
- The use of night length as a seasonal cue for responses such as flowering.
- Acclimation
- Morphological or physiological adjustment by an individual, within its lifetime, that offsets a stress-induced fall in performance.
Plant Signals, Timing and Stress Responses FAQ
How does auxin make a shoot grow towards light?
The tip senses light from one side and auxin is redistributed to the shaded side as it moves down to the elongation zone. Auxin activates proton pumps, acidifying and loosening cell walls, so shaded cells elongate faster than lit ones and the shoot curves towards the light.
Why is night length more important than day length for flowering?
The lectures identify night length, not day length, as the critical variable, so flowering tracks the longest uninterrupted period of darkness. A short-day plant flowers when the dark period outlasts its critical value, a long-day plant when the dark period is shorter, and a brief flash of red light in the middle of the night can change the response even though total darkness hardly changes.
How does acclimation differ from adaptation?
Acclimation happens within one individual's lifetime through changes in chemical composition, metabolic capacity or structure that restore performance. Adaptation happens across generations as natural selection changes the genetic make-up of a population, altering the phenotype that population inherently expresses. Priming sits beside both as a memory of earlier stress.
Can one part of a plant warn another about the environment?
Yes. Mature leaves exposed to shade or raised CO2 alter stomatal development in leaves that have not yet experienced the change, and chilling mature leaves switches on cold-response genes in distant warm meristems, so information travels systemically through the plant.
What are Grime's three plant strategies?
Grime classified environments by productivity and disturbance. Competitors dominate productive habitats, stress-tolerators dominate harsh habitats and ruderals dominate disturbed habitats, with most species falling somewhere between these three extremes rather than at a corner. Use them to explain why no single plant design suits every habitat.
Exam move
Treat this chapter as two maps. For signalling, write the general chain from environment to phenotype, then hang each example on it: phototropism, gravitropism, apical dominance, lateral roots and biomass allocation, noting which hormone carries each step.
For light and stress, make a table of the three photoreceptor families and what they detect, practise photoperiod predictions with invented schedules, and write one-line definitions of stress, priming, acclimation and adaptation with the timescale of each. Test yourself by explaining an unfamiliar plant response using the chain. Finish with one photoperiod and one acclimation question under time pressure.
Working through Plant Signals, Timing and Stress Responses in BIOL1030? Sia is AskSia’s AI Biology tutor — ask any BIOL1030 Plant Signals, Timing and Stress Responses question and get a clear, step-by-step explanation grounded in how BIOL1030 is taught and assessed. Read this chapter free, then take your hardest questions to Sia.
