1. 10. Plastids (from greek plastikos: “molded”)

- Chloroplast

- Amyloplast

- Leucoplast

- Chromoplast

Fig 1-43 Light micrograph of plastids with thin, tubular stromule extensions

Rapid Changes in plastid shape

1)All plastids are developmentally related to proplastids

Plastid developmental cycle and the inter-conversion of various plastid types

Fig. 1-45. TEM showing a proplastid (left) adjacent to a mitochondrion in a bean root cell

TEM illustrating phytoferritin deposits inside a proplastid in a root apical meristem cell of soybean

2) Amyloplasts are starch-storing plastids

: Unpigmented plastids that resemble proplastids but contain strach granules.

S: starch granules

TEM of amyloplasts containing many starch granules (S)

3) Several categories of plastid are named for their color

- Leucoplast are colorless plastids involved in the synthesis of monoterpenes, the volatile compounds

TEM showing leucoplasts (L) in an active secreting glandular trichome of pepperment.

Etioplast

TEM of an etioplast

PR: large prolamellar bodyT: associated unstacked thylakoids EN: envelope membrane

An early stage of grana thylakoid development in a greening etioplast

PR

PR: prolamellar body

Chloroplasts

GT: grana thylakoidsST: stroma thylakoids

Chromoplast (yellow, orange, or red….)

TEM of chromoplast of a ripe fruit of Jerusalem cherry.

The dense bodies in the plastid contain carotenoids (or xanthophylls)

4) The outer and inner membrane of the plastid envelope differ in composition, structure and transporter functions

Rich in galactolipids, poor in phopholipids

Out memebrane: nonspecific pore proteinpass size : 10 kd

Inner membrane: specific transporters pass small uncharged

5) The photosynthetic grana and stroma thylakoid membranes form a physically continuous three-demensional network

TEM depicting a single granum and associated stroma thylakoids

The spatial relationship between stacked granna and interconnecting stroma thylakoids

PS II

TEM revealing difference in grana and stroma thylakoids

PS I and ATP synthase

6) Plastids are partially autonomous, encoding and synthesizing some of their own proteins

7) Plastids reproduced by division of existing plastids

TEM of dividing etioplast

8) Plastids are inherited maternally in most flowering plants but paternally in gymnosperms

9) Plastids synthesize chlorophylls, cartenoids and fatty acids and reduce some inorganic nutrients

Mitochondria

: contain the respiratory machinery that generates ATP

TEM of a mitochondrion in a bean root tip cell

1)Similarity in the basic architecture of all mitochondria reflects the university of their mechanism for generating energy

An unusual phopholipid component of inner mitochondrial membrane

TEM depicting a longitudinal section through a transfer cell mitochondria

Arrows indicate ribosomes

2) Small solutes cross the outer and inner mitochondrial membranes sequencially,

whereas large proteins destined for matrix cross both membrane simultaneously

3) Mitochondria resemble prokaryotes in numerous important properties.

- Mitochondria possess the genetic capacity to make some of their own proteins.

- Mitochondrial ribosomes resemble those of prokaryotes.

- Mitochondria reproduce by fission.

TEM of a mitochondrion in a bean root tip cell, showing the final phase of division

4) Like plastids, mitochondria are semiautonomous and possess the genetic machinery to make some of their own proteins

Distinctive features of plant mitochondria genome

1. large size and complexity (about 10 fold larger than animal ones) 2. Genome: do not contain a set of tRNA genes (16 tRNAs specific to 12-14 amino acids)

3. Contains some chloroplast DNA sequences (tRNA genes, but not functional)