Lecture 16: Source sink interactions

Question 1

Three stages of crop production

Answer 1

1) Light - how light is absorbed
2) photosynthesis
3) Partitioning - how assimilates are partitioned into the harvested parts of the plant

Question 2

source:

Answer 2

• provider of assimilates
• -leaves (fully developed)
• -ears of cereals
• -other photosynthetic tissues

Question 3

Sink:

Answer 3

• utilises assimilates
• -young leaves and other developing tissues
• -roots
• -grains, tubers etc
• -all other non-photosynthetic parts of plant

Question 4

developing leaves are sources / sinks

Answer 4

sinks

Question 5

source sink manipulations:

Answer 5

• removal of leaves, ears, tubers etc
• grafting experiments
• physiological manipulation of sinks

Question 6

Carbohydrate metabolism in source cell:

Answer 6

In chloroplasts:
–calvin cycle produces:
=Fructose 6 - P changes to ADP-Glc and enters into starch granule
=triose-P which leaves chloroplast, changes into sucrose which leaves the source cell by sucrose transporter into the phloem

Question 7

Carbohydrate metabolism in sink cell

Answer 7

• sucrose is removed from the phloem via sucrose transporter
• changes to hexose-P
• enters amyloplast changes to ADP-Glc and enters starch granule

Question 8

Genetic manipulation of sucrose transporter in the phloem of potato. Antisense inhibition of the sucrose transporter (SUT1) in the phloem companion cells of potato results in:

Answer 8

• Lower photosynthesis
• increase in carbohydrates, shown by iodine staining of starch and crinkly leaves with lower chlorophyll
• lower efflux of sucrose form leaves
• fewer, smaller tubers

Question 9

enhanced sucrose loading improves rice yield by increasing __

Answer 9

-grain size!

Question 10

the transcript (mRNA) for Rubisco small subunit is called

Answer 10

rbcS

Question 11

Transcripts for rbcS decrease when cell suspension cultures are fed

Answer 11

Glucose

Question 12

growth at high CO2 can reduce

Answer 12

photosynthesis capacity in crop plants

Question 13

nitrogen allocation in rice & maize leaves:

Answer 13

a large part of nitrogen in a leaf is allocated to proteins involved in photosynthesis, such as Rubisco and light harvesting apparatus. This N need s to be moved to the seeds

Question 14

Source- sink interactions - NITROGEN

Answer 14

• nitrogen is mobilised to the grain throughout grain filling, and the rest of the plant senesces
• if the ear is removed, amino acids accumulate in the flag leaf

Question 15

cold girdling of petiole prevents

Answer 15

carbohydrate export

– cold girdling –> cold water circulating through copper tube

Question 16

effects of over expression of SPIKE in rice

Answer 16

a significant yield enhancement (13-36% grain yield) in IR64, plus improved plant architecture, without changing grain quality or growth period, achieved by expression of spikelet number from an Indonesian rice landrace.
- A spikelet = flower