Development of plant and ear until flowering

Development of plant and ear

Hordeum vulgare cv. Barke is a two rowed spring barley. In the greenhouse the development of the plant from seed to flowering takes about three month.

The first 4-6 fertile tillers of a plant usually flower within a few days (red label indicates flowering).

     

The diagram below shows the occurrence of anthesis in 55 ears from a group of ten plants. Flowering of a group usually finishes within 10-14 days.

       

Time frame of development and final caryopsis weight vary distinctly with the growing conditions. Weight and histological characteristics are used for correct staging of development. The age of the caryopses, measured in days after flowering (DAF) can only be used to compare caryopses from plants raised under the same conditions.


Staging of development (DAF):


The fresh weight of caryopses plotted against their age (DAF) results in a typical curve. Based on multidimensional screening of expression data three main phases of barley caryopsis development have been defined between 0 and 26 DAF: prestorage, intermediate and storage phase (Sreenivasulu et al. 2006, Plant Journal (47). They are reflected in the growth curve.


     
 

The inflorescence

Along the rachis, the main axis of the ear, three spikelets are situated at each node, alternating beetween the two sides. Each spikelet comprises one floret, two awned glumes and the rachilla. A floret is composed of the ovary, stigma, 3 stamens, two lodicules, palea and awned lemma. A section through the ear of the two-rowed cultivar "Barke" shows the dominant middle spikelet, two reduced lateral spikelets, the main axis (rachis) and the glumes. In the fertile floret the central ovary is surrounded by three anthers, the lemma and the palea.

About two weeks before flowering, female and male meiosis can be observed simultaneously in a floret. The section here shows callose in the anthers and division in a subepidermal cell of the nucellus. At this stage the integuments do not yet reach around the nucellus and the ovule is oriented almost at a right angle to the axis.


 

Flowering

At the time of flowering the barley ear is still mostly enveloped by the flag leaf sheat (boot) and only the tip of the awns is showing (upper arrow). Later the terminal internode will elongate and push the awn out of the sheat.

To determine time of anthesis, the leaf can be rolled back gently, the ear is freed, and a floret is removed and examined.

 

At flowering the anthers are yellow, the lodicules are swollen and the stigma branches are wide open and fully plumose. The left image shows the ovary of a floret about a day before flowering. The arrow points to one of the lodicules. At anthesis (see image on the right side and video below) the stigma is plumose and opens wide when the palea is lifted with tweezers. In "Barke" the florets belong to the closed flowering type, self fertilization takes place in the almost closed floret. The yellow anthers open at the top.

 

The development of the spikelets in the ear is not completely synchronous. Flowering starts first in the lower middle of the ear.

 

Pollen tube guidance

A special formation of the outer integument is instrumental in leading the pollen tube towards the micropyle. It is shown here in two longitudinal sections taken at rights angles to each other: