L3- grand challenges - photosynthesis

Question 1

what was the green revolution

Answer 1

1960-80s accumulation of agricultural advances, such as fertiliser and selective breeding to increase wheat yield

Question 2

what are the main grand challenges in plant biology

Answer 2

fertiliser is an energy demanding limiting resource
- crops need fertiliser - N,P,K
- K and P are non-renewable, mined resource
- synthesis of N fertiliser requires huge amount of energy and environmental cost

crop growth is increasingly limited, due to drought stress increasing, mild water stress reduce the rate of photosynthesis, 1kg rice needs 2500 litres of water

modern agriculture depnends upon widespread use of pesticides, herbicide and fertiliser, there is a changing face of disease, new variants, climate change leading to rapid spread of disease
wheat stem rust ug99 eg, 90% crop losses, no resistent wheat varieties, moving into major growing areas.

Question 3

what three things need to be improved in plants to face grand challenges

Answer 3

• improve photosynthesis
  -improve water-use efficiency
• improve nitrogen uptake

Question 4

how do plants undergo DNA sequencing

Answer 4

capillary sequencing (1980-2000)
DNA sequencer, 460,000 bases a day, slow and expensive human genome cost >10million and took yrs

next gen sequencing (2010 on)
sequencing on a chip, human genome cost 1000dollars ish and could sequence in hours

Question 5

how are plants genetically manipulated

Answer 5

highly effective methods

agrobacterium-mediated transformation

molecular biology and gene cloning synthesis

Question 6

what are the benefits of genetic manipulation

Answer 6

efficient methods for regen of plants after transformation and of direct transformation of reproductive tissue

gene editing techniques (CRISPR), allow precise and novel modification of genomes, this is exact not like old techniques which were more random

Question 7

what is state of GM crops

Answer 7

GM crops are now grown widely in N and S America and in parts of Asia - spectrum of crops are limited and evidence of pest and herbicide tolerance

but GM crops can lead to pest-resistance
Bt toxin leading to pest resistance
- Bt toxin from B thuringiensis, kills insects, bt gene transformed into maize, cotton

GM crops lead to herbicide tolerance
glyphosate inhibits aromatic amino acid biosynthesis
bacterial EPSP synthase is not inhibited by glyphosate
- transgenic plants express novel EPSP synthase is tolerant of glyphosate (round-up)
- round up ready crops= no till agriculture, decrease in totoal herbicide used (spectrum of herbicides also decrease)

Question 8

basics of photosynthetic reaction

Answer 8

there are light dependent reactions (plants absorbs photons, lgiht energy and converts it into chemical enerhy ATP)
and
light independent reactions (calvin cycle)

Question 9

what is important aspects of chloroplasts

Answer 9

thylakoid -
has ETC and ATP synthase for photophosphylation, chlorophyll here

stroma-
has appropriate enzymes for calvin cycle

Question 10

what is the process of photosynthesis

Answer 10

firs need to absorb light, this is done via light harvesting complexes (essentially chlorophyll, absorb photons of light)

light energy then shuttled down to a reaction centre, and here energy is used to split water to produce oxygen and excited electron

this excited electron is transfered to pheophytin from photosystem 2 (first photosystem), and then along the Electron transport chain (here a proton gradient is needed, so it can drive ATP synthase motor that ultimately make ATP), then to photosystem 1 PS1

electron goes to second photosystem, PS1. where electron has had its energy depleted, PS1 excited it and then shuttles it on proteims called ferredoxins

Question 11

whats the overview of imrpoving photosynthesis

Answer 11

photosynthesis involved the harvesting of light energy to chemical energy (ATP and NADPH), which are used to fix CO2 to triose phosphates from which a transportable sugar (sucrose) os formed which can be used to build biomass throughout the plant
- many of these elements appear to add inefficiency to the process, can they be engineered for improvement, only 3% of the light energy can be used as useable energy

Question 12

what is a main way to increase efficiency

Answer 12

excess light energy is absorbed by light harvesting complexes, but has nowhere to go
this can damage photosynthetic machinery, particularly PS2

this can be repaired but under extreme conditions causes photoinhibition and eventually photosynthesis stops

overexpression of D1 enzyme (involved in damage repair of PS2) protects from thermal damage and leads to increase biomass and yield in rice under control conditions- this can be done by manipulating the zeathanin/violaxanthin cycle (responsible for channeling extra energy out of plant), this leads to decreased light damage

Question 13

what is the zeaxanthin cycle

Answer 13

this is how plants avoid taking in too much light energy in

zeaxanthin turns to violaxanthin via ZEP, violaxanthin turn to zeaxanthin via VDE

ZEP speeds up the relxation of this (quicker to react to shade)
PsbS involved in repair of damaged photosynthesis

Question 14

what are the targets for improving photosynthesis

Answer 14

targets for improvign light-independent photosynthesis

-rubisco
-photorespiration
- regeneration of RuBP

Question 15

how does RuBisCO work

Answer 15

carbon dioxide and oxygen both compete for RuBisCO

high c02 levels favour photosynthesis
high O2 levels favour photorespiration (less efficient)

rubisco (ribulose 1,5 bisphosphate) and oxygen make
2-phosphoglycolate (cant be used in calvin benson)

2-phosphoglycolate can be CONVERTED to 3-phosphoglycerate (useful), but this results in LOSS of carbon overall

RuBisCO molecules vary in their structure between species, some are much better at distinguishing CO2 and O

Question 16

how can you decrease photorespiration

Answer 16

it excepts fact cant change rubisco, but tried to adjust environment around it
increase the CO2 local concentration around rubisco (decrease o2), this is via carbon concentrating mechanisms

this can be done via pyrenoids and caboxysomes, protein complex’s where rubsico is focused within the cell, this is evolutionary tactic that is found in algae and bacteria

the other way is also through inspiration by nature, this is by looking at C4 photosynthesis, this is where the cell type (bundle sheath, around the vascular tissue), here there is a system to localise rubisco in bundle sheath, and increase co2 within the cellm this is by initial fixation of co2 from an enzyme that does not undergo photorespiration it create a 4 carbon sugar, the co2 is released in neighbouring bundle sheath cell

Question 17

what example of plant that could be targeted by C4 mechanism

Answer 17

C4 rice
- rice is staple grain for 50% of earths population
- c3 plant
- low efficiency of conversion of light energy, due in part to relatively high photorespiration rates AND high nitrogen requirements

if rice could be engineered to be C4
- huge increase in yield (upto 50%)
-potential to grow it in more conditions
- potential to grow it over larger area

Question 18

how has C4 plants evolved

Answer 18

occurs in monocots and dicots
- evolved 62 independent times, evolved in low CO2 hot dry areas, multiple origins suggest convergent evolution
involves both biochemistry and leaf anatomy

Question 19

how does glycolate aid improving photosynthesis

Answer 19

rescue glycolate (product of photorespiration) and return it to calvin-benson cycle

during photorespiration co2 is fixed by rubisco, waist product is glycolate, which through manipulation can create transgenic plant in which the wait product phospho glycolate, is regenerate to form PGA molecules

Question 20

how else can photosynthesis be improved

Answer 20

• stimulating RuBP regeneration increase productivity and water use efficiency
• increased cell density leads to increased photosynthesis