Plant Development key terms

Question 1

Charyophycean green algae

Answer 1

closest living species to a possible land plant ancestor. Both share cellulose in their cell wall and have plasmodesmata. Coleochaete species have cell walls with lignin type polymers.

Question 2

Bryophytes

Answer 2

Non vascular land plants such as mosses

Question 3

Pteridophytes

Answer 3

Trachophytes (vascular plants). Seedless vascular plants such as ferns

Question 4

Gymnosperms

Answer 4

Trachophytes (vascular plants). Plants with pollen and naked seeds such as conifers.

Question 5

Angiosperm

Answer 5

Trachophytes (vascular plants). Flowering plants.

Question 6

Rhynie Chert

Answer 6

407 mil old geological site in scotland that preserves the most ancient known land plant ecosystem, including associated animals, fungi, algae and bacteria.

Question 7

Rhynia gwynne-vaughanii

Answer 7

Rhynia are a genus of Devonian vascular plants. This was one of the most common plants in the Rhynie ecosystem. Dichotomus branching where the apical meristem splits in two. They had a cuticle and stromata for preserving moisture and gas exchange. Rhizomal axes. Sproangium for reproduction.

Question 8

Cotyledon

Answer 8

Embryonic leaves that appear as a seed emerges, allowing seedlings to immediately photosynthesize.

Question 9

Hypocotyl

Answer 9

Embryonic stem

Question 10

Primordium

Answer 10

small cellular outgrowths that develop into lateral organs such as leaves and flowers

Question 11

Rib meristem

Answer 11

Region of the meristem just behind the central and peripheral zones. Here cells proliferate and develop into cells that comprise the stem.

Question 12

Phyllotaxis

Answer 12

Refers to the arrangement of lateral organs around a central axis. This relates to how the primordium is positioned around the shoot apical meristem. In some plants, this allows organs to be organised in a spiral shape, with each new organ being 137.5 degrees from the last. In some plants this is 180 degrees.

Question 13

KNOX1

Answer 13

Promotes meristem indeterminancy, allowing the SAM to constantly grow. STM in Arabidopsis. When mutated, the SAM becomes meristem and no true leaves are formed. When overexpressed, leaves become indeterminant and form knotts. This is the antagonistic relationship with ARP that promotes determainancy. STM causes expression of ITG, leading to the synthesis of Cytokinin.

Question 14

ARP

Answer 14

Known as AS1 in arabidopsis. It promotes determinancy in primordium. When mutated, leaves become indeterminant and form knotts, like when STM is overexpressed. Its antagonistic relationship with STM is shown in stm mutants, where AS1 is expressed in the SAM.

Question 15

Apical dominance

Answer 15

Where the central shoot apical meristem is dominant over the axillary shoots.

Question 16

Perianth

Answer 16

Collective word for the petals (corolla) and sepals (calyx) of a flower.

Question 17

Tepals

Answer 17

When sepals and petals are indistinguishable, they are termed tepals.

Question 18

Strobili

Answer 18

Reproductive organ for gymnosperms. Staminate strobili/mircostrobilus are the pollen producing male organ, which has its pollen dispersed by wind. This pollen is called a microspore, produced in the microsporangium brachts. Ovulate strobili/megastrobilus are the seed producing female organ. They produce the female gametophyte (megaspore) in the megasporangium brachts. Once pollen lands, it produces pollen tubes that move towards the gametophyte. Once fertilised, seeds are produced.

Question 19

Strobili (gymnosperm) vs Flowers (angiosperm)

Answer 19

Strobili have a captive gametophyte while flowers have an enclosed gametophyte (in ovule). Strobili have a naked ovule while flowers have an enclosed ovule, enclosed in carpel tissue making it harder for pollen to reach it but also protects it. Strobili male and female organs found on separate cones. Flower male and female organs can be found on the same flower.

Question 20

Clemantis inegrifolia

Answer 20

Basal eudicot with no true petals, rather having petal-like sepals. The ABC model would predict that the second whorl lacks B gene expression, therefore not overlapping with A, rather giving you two whorls of A gene (sepals). Clemantis inegrifolia has petaloid sepals while Celmantis chiisanensis has seperate whorls of petaloid sepals and petals. Thes two species of Clemantis differ by the presence of petals. B-class proteins were measured in both. AP3 was present in the flower buds of C. chiisanensis while not in C. inegrifolia. Therefore, the difference in B class gene expression may explain the difference in petal formation.

Question 21

Tulips

Answer 21

Tulips have petal-like tepals in theirs 1st and 2nd whorls. This would suggest that the B gene has expanded into the 1st whorl. It was found that Tulip B genes were expressed in whorls 1, 2 and 3.

Question 22

Basal angiosperms ABCE model

Answer 22

The ABCE model in basal angiosperms has leaking between whorls, having gradients rather than boxes of every gene. In the outer tepals there is strong A and B and some weak C expression. In the inner tepals there is weak A, strong B and weak C expression. In stamenoids there is weak B and strong C expression.

Question 23

Grasses (rice) ABCE model

Answer 23

Whorl 1 has A and E genes, producing lemma and palea. Whorl 2 has A, B and E genes, producing lodicules. Whorl 3 has A, B, C and E genes, producing stamens. Whorl 4 has A, C, C* and E genes, producing the carpel. C* is not a MADS box protein.

Question 24

Lodicule

Answer 24

The lodicule is a part of wind pollinated angiosperms that swells, causing the stamens to emerge, allowing cross pollination.

Question 25

Obligate Out-crosser

Answer 25

Can not self-pollinate. Need to attract pollinators. An example is Arabidopsis lyrata who’s own pollen is rejected.

Question 26

Opportunistic Out-crosser

Answer 26

Can self pollinate and out-cross.

Question 27

Predominant self-crosser

Answer 27

Mostly self pollinates, but is capable of being pollinated by other plants. Usually have smaller flowers as they do not need to attract pollinators, with the stamen positioned so it sheds pollen on the stigma. Arabidopsis thaliana has small flowers and can accept its own pollen, forming pollen tubes.

Question 28

Prevention of polytubey

Answer 28

The persistent synergid cell needs to be inactivated by fertilised ovules. Upon fertilisation of the central cell, the endosperm and the synergid cell fuse, disrupting pollen tube attraction. Upon egg cell fertilisation, ethylene signalling is activated. This initiates the disorganisation of the persistent synergid nuclei. During endosperm mitosis, chromosome condensation destroys the persistent synergid nuclei.

Question 29

Abscisic acid (ABA)

Answer 29

A hormone that suppresses growth during germination.

Question 30

Giberellin (GA)

Answer 30

A hormone that promotes growth during germination.

Question 31

Heat, fire and/or smoke as Germination signals.

Answer 31

Ceanothus Species. Seeds require heat, followed by cold in winter to germinate in spring. Over 100-year-old seeds are found to be viable, waiting for their next forest fire.
Papaver Californicum. Seeds require signals from smoke to germinate, meaning they germinate after forest fires. They can remain dormant for many years in the soil between forest fires.

Question 32

Dormancy to Germination

Answer 32

The first stage of seed development is called the maturation stage where the seed is mostly building up its reserves, synthesizing storage compounds such as starch, storage proteins and oil, while ABA increases. Eventually the seed ripens at peak ABA to form a dormant seed, which can stay dormant for many years. At this stage the seed is dessication tolerant, meaning it can lose water and dry up. Once the physical barrier is breached (seed is opened), the seed is hydrated, forming an imbibed seed. The imbibed seed can undergo secondary dormancy. The imbibed seed is coupled with increased expression of ABA. Signals such as light, cold, chemical suppression loss can break the dormancy of the imbibed seed. This leads to decreased ABA levels and increased GA levels, promoting germination and growth. ABA must go down for GA to go up.

Question 33

Germination

Answer 33

ABA prevents germination by inhibiting GA. GA is produced by the seed after imbition, but the seed is initially not to sensitive to GA due to inhibition from ABA. Light, cold and other signals can increase GA production and GA sensitivity by repressing ABA synthesis and promoting ABA catabolism. Eventually enough GA synthesis allows for ABA synthesis to be inhibited and ABA degradation by upregulation of ABA catabolism genes.